Cull mode

Minimum Inspector Level	Basic
Available since	1.0

Cull mode defines which faces of a mesh will be rendered (or, if we want to be picky, it defines which faces of a mesh will be culled, and therefore not rendered).

Off

Both front faces and back faces will be rendered (also called double sided).
Keep in mind that rendering both faces means you render twice the same mesh, so use it only where necessary, and even keep the double sided part of the mesh in a different material, so you will only need to apply it where is actually needed.

Front

Front faces will be culled, and so only back faces will be visible, and you will only see the internal side of a mesh.

Back

Back faces will be culled, and so only front faces will be visible, this is the default value since is the most commonly used.