Dynamic batching
Combining many small moving meshes on the CPU every frame to cut draw calls — worthwhile only when they are tiny.
Static batching cannot help objects that move, since their vertices would have to be re-merged constantly. The dynamic variant does exactly that: each frame the engine transforms the vertices of small same-material meshes into one buffer and issues a single call. Because the merging happens on the CPU per frame, it only pays off when the per-vertex transform work is cheaper than the draw-call overhead it saves — hence the tight vertex limits engines impose (Unity caps it around 300 vertices). For many small identical objects, GPU instancing is usually the better tool, drawing copies from one mesh without touching their vertices.