DotNetNukeDocs.com is no longer up and running as an editable Wiki. We encourage you to check out and contribute to the Wiki now hosted on DotNetNuke.com. http://wiki.dotnetnuke.com/
Tabs within DotNetNuke are actually commonly referred to as Pages.
Pages are unique URLs that are defined in the TABS table of the DNN database.
The layout of a page is controlled by a Skin, and the content for a page is provided through MODULES