The number of sub-meshes in the MeshData.
Each sub-mesh corresponds to a Material in a Renderer, such as MeshRenderer or SkinnedMeshRenderer. A sub-mesh consists of a list of triangles, which refer to a set of vertices. Vertices can be shared between multiple sub-meshes.
If the MeshData is writeable, you can set the number of sub-meshes using this property. If the MeshData is read-only, this property is read-only.
Additional resources: Mesh.subMeshCount, GetSubMesh, SetSubMesh, GetIndices, Mesh.AllocateWritableMeshData, Mesh.AcquireReadOnlyMeshData.