Tabs mark the different sections of a profile. 

The Info tab displays basic information like Birthday and Hometown, as well as interests and activities. The Info tab also lists all Groups the user is a member of, and all the Pages the user is a Fan of.

The Wall tab displays the user's interactions with friends (comments and messages) as well as status messages.

The Photos tab displays profile photos and albums.

The Boxes tab displays all of the applications and features not showcased elsewhere on the profile.

Other tabs.  Users can feature their Applications by creating a tab unique to that application.