Level of detail???

Level of detail is a technique in which objects are classed by importance so objects with less importance will have less detail meaning less polygons, this allows more detail to be added to more essential objects. Another way of using this technique would be like fogging, so this would include objects further away having less detail than objects closer. Level of detail is essential because too much detail, can affect the animation, because there is too much going through the pipeline, so this technique reduces down the amount the pipeline processes.This technique is used to limit the amount of polygons on screen at one time as there are sometimes restrictions.

For example; In this game the important objects are the characters the camera is following, the crowd in the background are not as important but are there too add more realism to the game, so if you were to get closer to the crowd, you will notice that the level of detail is considerably less compared to your character.