Increase triangle count by subdividing existing triangles
During a mesh refinement, the existing triangles are split into smaller triangles until all triangles meet the threshold edge length requirement. The shape of the part is not adjusted by this operation, but it can be particularly useful for smoothing operations which require a more refined mesh.
Refine Triangle Mesh.
Select whether to refine only those areas composed of triangles that are currently selected.

A mesh refinement is applied to the selected surfaces of the cube.