​ From mesh

The Mesh command creates a polygon mesh from a NURBS surface, polysurface, or SubD.

A mesh is a collection of vertices and polygons that define the shape of a polyhedral object. Rhino meshes consist of triangles and quadrilaterals.

Rhino creates triangles and quadrilateral meshes for exporting to various file formats. If a mesh is generated from a solid, it will be seamless and watertight.

The meshes created by the Mesh command are editable and separate from the objects from which they were created. The meshes created by shaded viewport display modes are not editable. They can be extracted with the ExtractRenderMesh command.

For more information, please refer to the Rhino documentation.