From BlenderWiki

Page status (reviewing guidelines) Page reviewed and in good shape

Mesh Subdividing Tools

Subdividing adds resolution by cutting existing faces and edges into smaller pieces. There are several tools that allow you to do this:

Subdivide

Divide a face or edge into smaller units, adding resolution.

Loop Subdivide

Insert a loop of edges between existing ones

Knife Subdivide

Cut edges and faces interactively

Bevel

Subdivides edges or vertices, making them faceted or rounded