Job satisfaction is the level of contentment that a person feels towards his/her job, i.e., the extent to which people like or dislike their jobs). It is an important stimulus for professional career growth and it is generally associated with a person's ability to perform the required tasks, the level of communication within an organization, and the way managers treat their employees.
Job satisfaction is important because it is correlated with performance and productivity at work ... The higher the job satisfaction the higher the performance was and the successful relationships between colleagues are good
Job satisfaction is generally a self reported notion, measured using a large number of items on some sort of Likert scale. It refers to things such as satisfaction with salary, ability to related with your job and what you produce, and general work environment about collegiality and support.
Sometimes job satisfaction can not be achieved(completely) due to many external competing forces, as being satisfied is very intrinsic, intangible phenomenon and intangible things are hard to measure.
Satisfaction/happiness occurs when a reality or reward meets an expectation. Humans have an instinct need for growth (better than before). Organizations should thus continue to provide a fair opportunity for their employees to growth their career in order to keep them.