Nanite

Nanite is Unreal Engine 5's virtualized geometry system that renders massive polygon counts in real time by streaming only the detail the eye can perceive.

Nanite eliminates traditional polygon budgets and manual LOD (Level of Detail) creation. It processes billions of triangles by intelligently scaling geometric detail based on pixel density: if a mesh contains 10 million polygons but only occupies 500 pixels on screen, Nanite clusters the data to match that resolution. This allows developers to import cinematic-quality ZBrush sculpts or high-res Photogrammetry scans directly into the engine without performance-killing draw calls. It handles the heavy lifting of geometry streaming and culling (frame by frame) so artists can focus on visual fidelity instead of technical optimization.

https://docs.unrealengine.com/5.0/en-US/nanite-virtualized-geometry-in-unreal-engine/