Level Of Detail(LOD) is a type of culling, when a game replaces a high polygon count object(high qaulity) with a lower polygon count (lower qaulity) object, the replacing of the object is based on the distance of the camera(further away = low qaulity and closer = high qaulity) since the object is farther away the playee won't notice that it make a lower qaulity object this helps not use much proccesing power since it doesn't have to load detailed objects all the time, the amount of objects you can do for LOD can be 2 one high qaulity and another low quality but it doesn't look as smooth as a transition so it's better to use 3 to 6 models that range from high to low qaulity but it does take up more space when you add more models for LOD and takes more time to make all of them

the example above this text shows three objects with the one on the left being low qaulity, the one in the middle is the medium qaulity and the one on the right being the highest qaulity