Doc:Glossary/Subdivision Surface

Subdivision Surface

Is the tool which subdivides your model at render-time, without affecting your mesh at design-time. There are two subsurf algorithms in blender to choose from - Simple Subdiv, which doesn't affect the shape of your mesh, and is used to add detail to displacement mapping or render-time radiosity, both of which operate on a per-vertex basis. The other is Catmull-Clark, a common subdivision algorithm which smooths out curves, and allows you to make complicated smooth surfaces (eg people, plants, etc) with very few faces. However this algorithm can sometimes (read: often) have strange results with meshes containing triangles or verticies with many edges ("poles"), unless it is correctly handled.

Also called: Subsurf.