The forest is a complex ecosystem consisting mainly of trees that buffer the earth and support a myriad of life forms.

The trees help create a special environment which, in turn, affects the kinds of animals and plants that can exist in the forest. Trees are an important component of the environment. They clean the air, cool it on hot days, conserve heat at night, and act as excellent sound absorbers.

Plants provide a protective canopy that lessens the impact of raindrops on the soil, thereby reducing soil erosion. The layer of leaves that fall around the tree prevents runoff and allows the water to percolate into the soil. Roots help to hold the soil in place. Dead plants decompose to form humus, organic matter that holds the water and provides nutrients to the soil. Plants provide habitat to different types of organisms. Birds build their nests on the branches of trees, animals and birds live in the hollows, insects and other organisms live in various parts of the plant. They produce large quantities of oxygen and take in carbon dioxide. Transpiration from the forests affects the relative humidity and precipitation in a place.

A forest is a large area dominated by trees. Hundreds of more precise definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing and ecological function.

It must have a tree canopy

A forest is a piece of land with many trees. Many animals need forests to live and survive.

Forest can be defined as the large area of land covered with trees or there will be absence of trees with pre-dominantly other land uses.The trees in the forest should be able to extend upto a minimum height of 5 meters in in-situ. The area to be called as the forest must have an area of 0.5 hectares atleast and the canopy of more 10%.Forest do not includes the land that is mostly agriculture and under land uses.

Forest is a plant community predominantly of trees and other vegetation, usually with a closed canopy. Legally it is an area proclaimed to be a forest under a forest law.

It may be also defined as an area set aside for the production of timber and other forest produce, or maintained under woody vegetation for certain indirect benefits.

If I am not mistaken, FAO has a definition of forest that tries to cover many circunstances around the globe (page 3 of Forest resources Assessment 2015: Terms and Definitions)

http://www.fao.org/3/ap862e/ap862e00.pdf

However, I guess a suitable definition of forests at global scale depends on your goals. Have a look at this paper if you are interested:

"When is a forest a forest? Forest concepts and definitionsin the era of forest and landscape restoration"

https://link.springer.com/article/10.1007%2Fs13280-016-0772-y

There are hundreds of definitions of a forest. That's because it's a complex ecosystem that it's hard to characterize it in just few lines. For the sake of simplicity, a forest is an area that is not savannah nor a desert where trees are more predominantly abundant and compactly spaced along with undergrowth plants.

Something to consider: many species in scrub habitats, particularly Florida Scrub (e.g. saw palmetto, Lyonia spp., Quercus spp.) can be considered underground trees. Saw palmettos in particular have been shown to likely be thousands of years old although most of their biomass is stored underground as an adaptation to frequent fire return intervals. So these could be considered underground old-growth forests.

I think there are different definitions for forest to define forest cover in different areas with various climates.

Based on FAO :

Forest is determined both by the presence of trees and the absence of other predominant land uses. The trees should be able to reach a minimum height of 5 meters.

2. Includes areas with young trees that have not yet reached but which are expected to reach a canopy cover of at least 10 percent and tree height of 5 meters or more. It also includes areas that are temporarily unstocked due to clear-cutting as part of a forest management practice or natural disasters, and which are expected to be regenerated within 5 years.

But i think that it's not true for all regions

Forest, complex ecological system in which trees are the dominant life-form.

The world is full of secrets and one of them is the forests, which concentrate more than half of the biodiversity of terrestrial life on the planet. At the same time they function as a reservoir of carbon dioxide for all living beings that inhabit it. From the deepest layers of the earth to the tops of the treetops, forests are our heroes because they keep our planet healthy, and all of us alive. In addition, they are home to about 80% of all forest species, supply 75% of the planet's fresh water, generate chemicals that make up 75% of pharmaceuticals, influence the climate, moderate the daytime air temperature range and maintain atmospheric humidity levels. They also absorb carbon from the atmosphere and replenish oxygen in the air we breathe. The conservation of forest resources in watersheds that provide water for regions, health services and human consumption is an important component of strategies to supply their fresh, crystal-clear water that flows down from the mountains and into each of their homes. When balanced land use is undertaken in watersheds, forests absorb excess rainfall and then gradually release it. Forests are indispensable because they regulate the flow of water courses by intercepting rainfall, absorbing water from the underlying soil and gradually releasing it into the water courses and rivers of their basin, thus minimizing both flooding downstream and drought conditions. The forest cover retains soil moisture, providing shade that reduces evaporation loss caused by the exchange of radiant energy with the atmosphere. They are a barrier against erosion, landslides and avalanches. Tree roots give the soil the structure it needs to absorb and retain water when it rains, thus preventing flooding that would otherwise wash away the perfectly fertile soil we need to grow food. They provide a wide range of benefits such as clean water, shelter for breeding species, erosion and flood control, opportunity for recreation, and great diversity of species as well as reducing natural disasters.

Translated with www.DeepL.com/Translator (free version)

All of the above answers covers the term forest

Usually a forest is an area covered with high density of trees and under growths. But today, a forest is any land managed for the diverse purposes of forestry whether covered with trees, shrubs herbs etc. or not.

FAO has a basic definition, but as the answers above reflect (and I agree) there are as many definitions as trees. For me a few trees close by are a forest. In Paraguay by the Forestry Law (422/73) you need at least 2 hectares of trees to call it a forest and that has terrible consequences on management.Each country and even State eventually has it's own definition of forest in the environmental legislation.

George Mitri can refer to http://edugreen.teri.res.in/explore/forestry/what.htm

https://data.opendevelopmentmekong.net/dataset/1937c446-b07f-4fba-a577-1f299da1cced/resource/e70454d6-ff1c-4eeb-b988-ac40cfc5ca3f/download/venkateswarlu.pdf

The forest is the lung of the earth, and it is a term given to large groupings of plants, weeds and trees that extend to great areas of greatness, and thousands of animals and various insects live in them.

Forest is an area set aside for the production of timber or any other forest produce or maintained under woody vegetation for certain indirect benefits it provides (Forestry definition)

Forest is a collection of all forms (trees, trubs, shrubs, climbers.creepers, herbs, fungi) of plant life including micro and macrofauna and maintained for conservation and preservation of nature (Botanical)

Forest is an area proclaimed to be a forest under forest law (Legal definition).

Its from my understanding and gained knowledge

Forest is a diversity of small and large organism of plants animals which have benefit

UNFCCC, 2001

Forest' is a minimum area of land of 0.05-1.0 hectares with tree crown cover (or equivalent stocking level) of more than 10-30 per cent with trees with the potential to reach a minimum height of 2-5 meters at maturity in situ. A forest may consist either of closed forest formations where trees of various storeys and undergrowth cover a high proportion of the ground or open forest. Young natural stands and all plantations which have yet to reach a crown density of 10-30 per cent or tree height of 2-5 meters are included under forest, as are areas normally forming part of the forest area which are temporarily unstocked as a result of human intervention such as harvesting or natural causes but which are expected to revert to forest.

UNEP/CBD/SBSTTA, 2001

Forest is a land area of more than 0.5 ha, with a tree canopy cover of more than 10%, which is not primarily under agricultural or other specific non-forest land use. In the case of young forests or regions where tree growth is climatically suppressed, the trees should be capable of reaching a height of 5 m in situ, and of meeting the canopy cover requirement.

FAO 2000a (FRA 2000 Main Report)

Forest includes natural forests and forest plantations. It is used to refer to land with a tree canopy cover of more than 10 percent and area of more than 0.5 ha. Forests are determined both by the presence of trees and the absence of other predominant land uses. The trees should be able to reach a minimum height of 5 m. Young stands that have not yet but are expected to reach a crown density of 10 percent and tree height of 5 m are included under forest, as are temporarily unstocked areas. The term includes forests used for purposes of production, protection, multiple-use or conservation (i.e. forest in national parks, nature reserves and other protected areas), as well as forest stands on agricultural lands (e.g. windbreaks and shelterbelts of trees with a width of more than 20 m), and rubberwood plantations and cork oak stands. The term specifically excludes stands of trees established primarily for agricultural production, for example fruit tree plantations. It also excludes trees planted in agroforestry systems.

For FAO, the definition of the forest, or forest land, is based on the structure of the formation (percentage of tree cover, height of woody species) and its surface. ... The forest fallow system is an intermediate class between forests and non-forest lands.