HLOD
Merged proxy for distant groups of meshes
Also known as: Hierarchical LOD · Proxy mesh · HLOD layer
Definition
HLOD, or Hierarchical Level of Detail, replaces a group of distant objects with one merged proxy mesh and material, so the engine draws one object instead of hundreds. Normal LODs simplify a single mesh as it moves away, while HLODs simplify whole clusters such as a village or the edge of a forest, which is where most draw calls are saved in big worlds. In Unreal Engine 5 they are built per cell with World Partition.
In production
Set up HLOD layers in World Partition and build them as part of your pipeline, since they are generated data that must be rebuilt after changes. Clean, closed meshes with reasonable material counts produce better proxies. Check the transition distance so you do not see a visible pop, and compare the cost of the proxy with what it replaces, since a heavy proxy can be worse than the objects it stands for.