Floor area ratio (FAR) is a measure of the amount of floor space in a building relative to the size of the lot on which the building sits. It is usually expressed as a ratio, such as 2:1, which means that for every 2 square feet of land, there is 1 square foot of floor space. FAR is often used as a tool for zoning and land-use planning, as it can help to control the density of development and ensure that buildings are not too tall or too large for the area in which they are located.
FAR limits may be different in different areas and Cities. It's a way to make sure that a building will not take over the whole lot and leave no space for greenery, open spaces, etc. in a neighborhood, or to have a different approach to high-density areas ( like city center) and low-density area (like rural district)
It's worth to keep in mind that a low FAR does not mean it's bad for the environment or urban design, it's about finding a balance.