Special pages are pages that are created by the software on demand. They are located in their own namespace Special: and are not editable directly as other pages.
Some special pages depend on the preferences that have been set by a user, e.g. the number of titles which is displayed on a user's watchlist.
List of special pages
Clicking the link Special:Specialpages will take you to a list of all special pages on a wiki. Such a link is often accessible in the toolbox on the left hand panel.