Foliage rendering
The umbrella name for the techniques that draw large amounts of grass, trees and bushes without choking the frame rate.
A field of hundreds of thousands of grass blades or a forest of a thousand trees can't be drawn one object at a time. Foliage rendering therefore leans on GPU instancing for identical meshes, LOD chains that simplify with distance, and billboards or impostors that replace far trees with flat images. Leaves are often drawn as alpha-tested cards rather than modelled geometry.
Add to that wind animation in the vertex shader, which sways blades and branches with no extra draw calls, and GPU-driven culling that discards whatever won't be seen anyway. Crysis (2007) set the bar for dense interactive vegetation, and middleware like SpeedTree turned the technique into an off-the-shelf product. It remains one of the classic places a game trades fidelity for speed.