Based on your own quoted definition from Oxford Dictionary (see number 1), a scientist, professor, teacher, doctor, businessman, farmer or any other person 'who leads a group' is a leader. And a politician who doesn't lead any particular group is not a leader. In short, anybody can be a leader. However, not all can actually lead.

Not only politicians, but anyone who has the qualities of a leader can be a LEADER.

Dear Colleagues,

Good Day,

"Definition of a Leader

A leader is "a person who influences a group of people towards the achievement of a goal". A mnemonic for this definition would be 3P's - Person, People and Purpose as illustrated by the following diagram.

Person

Is leadership a position of office or authority? Or, is leadership an ability in the sense that he is a leader because he leads? We all may know or hear of people who are in positions of leadership but who are not providing leadership. A position of office is no guarantee of leadership but it helps in the sense that a leadership position usually commands a listening ear from its people and that is a good starting point for anyone who desires to be a leader.

A leader by its meaning is one who goes first and leads by example, so that others are motivated to follow him. This is a basic requirement. To be a leader, a person must have a deep-rooted commitment to the goal that he will strive to achieve it even if nobody follows him!"....

Please, see the link for detail....

http://www.vtaide.com/gleanings/leader.htm

Dear Colleagues,

Good Day,

"What is Leadership?

Leaders are people who do the right thing; managers are people who do things right.– Professor Warren G. Bennis

Leadership is the art of getting someone else to do something you want done because he wants to do it.– Dwight D. Eisenhower

The word "leadership" can bring to mind a variety of images. For example:

A political leader, pursuing a passionate, personal cause.

An explorer, cutting a path through the jungle for the rest of his group to follow.

An executive, developing her company's strategy to beat the competition.

Leaders help themselves and others to do the right things. They set direction, build an inspiring vision, and create something new. Leadership is about mapping out where you need to go to "win" as a team or an organization; and it is dynamic, exciting, and inspiring. 

Yet, while leaders set the direction, they must also use management skills to guide their people to the right destination, in a smooth and efficient way.

In this article, we'll focus on the process of leadership. In particular, we'll discuss the "transformational leadership" model, first proposed by James MacGregor Burns and then developed by Bernard Bass. This model highlights visionary thinking and bringing about change, instead of management processes that are designed to maintain and steadily improve current performance."

Please, see the link....

https://www.mindtools.com/pages/article/newLDR_41.htm

Dear Colleagues,

Good Day,

"What is "Leadership" and What Makes a Good Leader?

There are many definitions of leadership. The Collins English dictionary defines leadership as “the leader(s) of a party or group.” Yet true leadership is much more than that. A leader can be the CEO of an organization, or a first year employee who leads his or her team to success behind the scenes. A leader might lead through official authority and power, yet just as often great leaders lead through inspiration, persuasion and personal connections.

So what is leadership? One great definition is:

“Leadership is the art of leading others to deliberately create a result

that wouldn’t have happened otherwise.”

It’s not just the creation of results that makes good leadership. Good leaders are able to deliberately create challenging results by enlisting the help of others. They can single handedly turn failing companies into Fortune 500 organizations. They can change company cultures. Good leadership is an essential key to corporate success.

The Characteristics of a Good Leader

What makes a good leader? Here are some of their most important characteristics:

• Self-Awareness.
• Self-Direction.
• Vision.
• Ability to Motivate.
• Social Awareness.

Please, see the original article for more information.....

https://siyli.org/what-is-leadership-what-makes-good-leader/

Romer Castillo answered your question very well. And you can be a leader as well without any need to be a politician, you only have to study, read carefully what you encounter every day and exercise your leadership over a group.

If your actions inspire others to dream more, learn more, do more and become more, you are a leader.

--- John Quincy Adams

The one that sees and does when the others don't do anything except keeping their eyes shut and go with the flow.

The definition 1 of the leader in Concise Oxford English Dictionary, quoted in the question, partially means "the person who leads a country." Here, "leads a country" presupposes political leading. In this sense, politicians can be leaders. However, in the general sense, leaders exist in every field of human activity. Further, among political leaders of countries, there have been persons who were a scientist.

A leader is best when people barely know he exists, when his work is done, his aim fulfilled, they will say: we did it ourselves.

---Lao Tzu

Anybody may become a leader.Current Germany Chancellor is PhD in physics

In developed country: Leaders are responsible for their actions

Developing country:Leader has a private life and not answerable

I agree with everyone's comments but i believe everyone has the potential to be a leader so far we are ready to serve 

A leader is a person who can motivate peoples to do things toward his vision, everyone can be a leader

Because leadership is not a rational activity but sentimental.

Following explanation of " Leader" I do not agree that mentioned professons and activities will not represent the leaders

Barbara,

I used to think that this problem is only peculiar to my environment alone. I strongly agree with you that we need "fishing expeditions" for potential leaders. OUR WORLD NEEDS URGENT ATTENTION to change things before they get out of hand.

Dear Mahamad,....

in principle everybody can be a leader.

It means there must be a group acceptings the leadership of a special person. This acceptance is coupled to special skills and the abilities of this person. He must be able to convince the group that he is acting in their interest having the talent solving problems, critical situations and realizing visions for improvement. 

This must result in an advantage for the group strongly coupled with a direct exchange of the leader with the group members and their interests. In a group with a good leader there is no room for upcoming conflicts based on permanent discussions about fundamental proceedings.

Political leadership based on this principles is difficult and often impractical.

With best regards

Michael

I think anyone can assume a position of leadership, in their jobs, school study groups, families, club associations and so on.

BUT!

In a democracy, the politicians are supposed to be implementing what the electorate tells them to do. I know that politicians like to call themselves "leadership," and that's actually part of the problem. Not just that politicians have the wrong idea about their job, but that the voters are so complacent and lazy, as to let them get away with it.

In a democracy, people must not let themselves slide into this type of complacency, where they think the politicians' job is to spoon-feed the masses. "Leadership," applied to politicians, means to organize and arrange how to implement what they were voted in office to do. By the voters. That's the meaning of "public servant."

Hello Mahamad,

In my opinion, a person who has Leadership skills could be Leader. 

Regards,

we have to distinguish the meaning of leader , I think, it means the influential, effectual, and notable person. these features may be available in some people  in different tasks, like art , sport, science, trade, politics, etc. in general, we call the president or P.M the leader, but in fact, the leader exists in each task of the life, as I said, previously.

leader word basically means the person who leads others. A politician is a representative of a selective population. We have leaders in every walk of life. there are organisational leaders, social leaders. In words of APJ Abdul Kalam (Ex President of Indea and great scientist) "Good leader is one who gives the credit of success to his team members and bears the responsibility for the failure"

Dear Colleagues,

Good Day,

“Leadership is being the first to put others second. Wait, that’s not right. That’s politics.”

                                      ― Jarod Kintz, This Book is Not FOR SALE

I think a LEADER is one who always lead by an EXAMPLE not merely delivering popular speeches. Most of the people have very short term memory regarding what they listen to. Because of this, they very easily forget and forgive those political leaders who always lie and make them fool. Also, people can be easily divided on the basis of religion, cast, social barriers, etc. So, people always make someone HERO who only shows the day light dream and who always speak on a topic which is favorable for people. 

On the other hand, scientist, engineers, doctors, etc. always work for the tasks which are very much concrete and really useful. They do not deliver popular speeches like politicians. They do not try to excite some group of people against other group. Also, such people have less public platform to show their usefulness towards the society.

But politicians, movie-actors, cricketers and other sports personalities always remain in lime-light through media. So, very easily people identify them as their role model.

Dear Chintan Patel,

I am really impressed with your answer. Actually our society mistakenly  terms politicians as leaders who are mostly biased for social welfare. On the other hand, scientists, engineers, doctors, farmers etc are the actual leaders who are working continuously for the social welfare. In real sense these persons are the REAL LEADER not the politicians. 

Dear Mahamad Nabab Alam

In this kind of situations, the role of a teacher (school, college, etc) is very much important to train and teach the students about this. Only through teaching the students we can set the right persons on the right position.

Dear Chintan Patel,

I am fully agree with you. 

Who is a leader? Is politicians leader? Why scientists, professors, teachers, doctors, businessmen, farmers etc. are not leaders?

Think a leader can be anyone as long as s/he can influence follower(s) to achieve certain goal(s) in an environment.  You can see how these 4 elements are related in my diagram found in the following RG link:

https://www.researchgate.net/post/What_is_the_best_definition_of_a_leader

The Real Leader is very kind, brave, not selfish, has good personality,  and can lead the Authorized Mechanism towards the Best Benefits of People and the Country. 

I see that there are a lot of Leaders who has the background of Scientists, Professors, Teachers, Doctors and Businessmen.

Dear Colleagues,

Good Day,

"A leader is judged not by the length of his reign but by the decisions he makes."

                                                                           ----   (Klingon Proverb)

Dear Colleagues,

Good Day,

"He that would be a leader must be a bridge."

                                                          -----  (Welsh Proverb)

Leader is the person who meets a set of features and capabilities that allow you to influence how we think and act in a certain group of people, can take the lead and guide the action of the group towards achieving defined goals. Leadership does not necessarily mean an inequity in the power of the group, although often this happen. When the cause is a matter of a general nature, affecting the whole society, the leader can be called a political leader, but when addressing the action is oriented to the achievement of other purposes, scientific, educational, health, economic, the leaders can not necessarily be qualified as political, but as project managers or orchestra, spiritual guides, teachers, entrepreneurs, businessmen, producers or used one more of many possible epithets.

Dear Colleagues,

Good Day,

"A leader is one who knows the way, goes the way, and shows the way."

                                                                         ----  John C. Maxwell

Dear Colleagues,

Good Day,

"Innovation distinguishes between a leader and a follower."

                                                               -----   Steve Jobs

Dear Colleagues,

Good Day,

"For one mission, there is one leader."

                                        -----  (Klingon Proverb)

The Leader is a person who can lead his organization towards the sustainable benefits by Smart Strategy.

A politician not necessarily a leader. A person who is a role model and has followers (as a result of his actions).

For example, the Brazilian president whose leadership is officially in doubt cannot be referred to as a leader.

Dear Colleagues,

Good Day,

"A political leader is necessarily an imposter since he believes in solving life's problems without asking."

                                                                     ----   Andre Malraux

Dear Colleagues,

Good Day,

"The task of the leader is to get his people from where they are to where they have not been."

                                                                  ---- Henry Kissinger 

Dear Colleagues,

Good Day,

"Leadership has a harder job to do than just choose sides. It must bring sides together."

                                                                                            ---- Jesse Jackson

"When you put together deep knowledge about a subject that intensely matters to you, charisma happens. You gain courage to share your passion, and when you do that, folks follow"

                                                                                            --- Jerry Porras

Some Leaders are Engineers or Innovators.    

When we accept any person as a reader we find his qualities , contribution , his mode of thinking & behavior ,& also his contribution in his respected areas .If we find a leader of such quality which we have accepted from our within such leaders receive the position of respect from the persons concerned .

With this we proceed with the quality of leaders where our teachers & professional personnel including medical professional personnel are all coming in categories of leaders . They may not be having the mob of political leaders but for relative groups of all person who are contacting their association person,they go with their respect & either salute them or are keeping them with fore headed hands such persons command a respect which remains ever lasting & may not come in the categories of political leaders who leadership are counted with mob or so to say number of heads .

Right from teacher to the persons of any professional career including doctors with whom we come in contact & receive that beneficial & grace such person get the place in our heart as a respectable person who are more than leaders.

If not out of way to sight & small example of my personal experience that some years back i receive an opportunity to meet my primary school teacher ( at that time aged ) I went approach him with fore headed hands & with his staring eyes , he humbly asked me i could not recognize you & i gave my small background i was your student & gave the reference e of my daddy & he could recognize me with a very nice feeling which i observed in his eyes & reciprocate with my eyes in my loving face we parted with each other .

In our culture either a teacher or such other person with whom we receive the grace & kindness for our action we respect them not as a leaders but so to say Our Guru ( Teacher) .

For political leaders their respected because of their contribution & also for establishing a welfare atmosphere for their citizen in every part of the country . It is  a fact that all political leaders have not become the messenger for the peace of people & so during my earlier days i have come across a version for politician '' Power corrupts Power ,Absolute power corrupts Absolutely '' 

This is my personal opinion 

''The most powerful leadership tool you have is your own personal example''

                                                                                                  --- John Wooden

Leaders in Politics are political leaders, otherwise Leaders are there everywhere. In fact, the leaders like Dr APJ Abdul Kalam, Swami Vivekananda, Mahatma Gandhi, and many others in different fields such as science, engineering, research, education, etc. are BETTER leaders than most of the political leaders. Moreover, the leaders of these fields should adhere to lead in politics, rather they should focus on existing roles so that mass could be benefited with the knowledge of science, research etc so that socio-economic development of the society is further elevated.

Dear Colleagues,

Good Day,

“Innovation distinguishes between a leader and a follower.”

                                                                                                     ~STEVE JOBS

''The nation will find it very hard to look up to the leaders who are keeping their ears to the ground''

                                                                         — Sir Winston Churchill

"According to Research by asaecenter, leadership style is the way a person uses power to lead other people. Research has identified a variety of leadership styles based on the number of followers. The most appropriate leadership style depends on the function of the leader, the followers and the situation.

Some leaders cannot work comfortably with a high degree of followers’ participation in decision making. Some employers lack the ability or the desire to assume responsibility. Furthermore, the specific situation helps determine the most effective style of interactions. Sometimes leaders must handle problems that require immediate solutions without consulting followers.

What are Different Leadership Styles?

We have covered 12 different types of ways people tend to lead organizations or other people. Not all of these styles would deem fit for all kind of situations, you can read them through to see which one fits right to your company or situation.

1. Autocratic Leadership

Autocratic leadership style is centered on the boss. In this leadership the leader holds all authority and responsibility. In this leadership, leaders make decisions on their own without consulting subordinates. They reach decisions, communicate them to subordinates and expect prompt implementation. Autocratic work environment does normally have little or no flexibility.

In this kind of leadership, guidelines, procedures and policies are all natural additions of an autocratic leader. Statistically, there are very few situations that can actually support autocratic leadership.

Some of the leaders that support this kind of leadership include: Albert J Dunlap (Sunbeam Corporation) and Donald Trump (Trump Organization) among others.

2. Democratic Leadership

In this leadership style, subordinates are involved in making decisions. Unlike autocratic, this headship is centered on subordinates’ contributions. The democratic leader holds final responsibility, but he or she is known to delegate authority to other people, who determine work projects.

READ  Sample Thank You Email after Job Interview

The most unique feature of this leadership is that communication is active upward and downward. With respect to statistics, democratic leadership is one of the most preferred leadership, and it entails the following: fairness, competence, creativity, courage, intelligence and honesty.

3. Strategic Leadership Style

Strategic leadership is one that involves a leader who is essentially the head of an organization. The strategic leader is not limited to those at the top of the organization. It is geared to a wider audience at all levels who want to create a high performance life, team or organization.

The strategic leader fills the gap between the need for new possibility and the need for practicality by providing a prescriptive set of habits.  An effective strategic leadership delivers the goods in terms of what an organization naturally expects from its leadership in times of change. 55% of this leadership normally involves strategic thinking.

4. Transformational Leadership

Unlike other leadership styles, transformational leadership is all about initiating change in organizations, groups, oneself and others.

Transformational leaders motivate others to do more than they originally intended and often even more than they thought possible. They set more challenging expectations and typically achieve higher performance.

Statistically, transformational leadership tends to have more committed and satisfied followers. This is mainly so because transformational leaders empower followers.

5. Team Leadership

Team leadership involves the creation of a vivid picture of its future, where it is heading and what it will stand for. The vision inspires and provides a strong sense of purpose and direction.

Team leadership is about working with the hearts and minds of all those involved. It also recognizes that teamwork may not always involve trusting cooperative relationships. The most challenging aspect of this leadership is whether or not it will succeed. According to Harvard Business Review, team leadership may fail because of poor leadership qualities.

6. Cross-Cultural Leadership

This form of leadership normally exists where there are various cultures in the society. This leadership has also industrialized as a way to recognize front runners who work in the contemporary globalized market.

Organizations, particularly international ones require leaders who can effectively adjust their leadership to work in different environs. Most of the leaderships observed in the United States are cross-cultural because of the different cultures that live and work there.

http://wisetoast.com/12-different-types-of-leadership-styles/

Dear Mahamed

Every one can be a good leader, father, teacher, first brother or sister in the family  and captain and so on........The leadership is a skill can not found in any one depending about personality characters...So every one could be a leader..

Thanks a lot  

I thinking the meaning of the leaders depending on the culture of of the community 

The leader is the person who can see the way and guide others to it. That means he have the ability to convince other. The scientific or academic level is not the only prerequisite for leadership.

Regards

SM Najim

Dear Colleagues,

Good Day,

Leaders don't inflict pain - they share pain.

                                                                         ----  Max Depree

A politician lead group of people and are elected by people.  Then only politician is a leader.

Dear Colleagues,

Good Day,

Attached is an excellent  presentation which entitled: "How to be a good leader", see the link, please.

https://www.slideshare.net/SamBrandt1/how-to-be-a-good-leader-52541957