http://msdn.microsoft.com/en-us/library/ms431831.aspx
Absolute URL that specifies a full path and that begins by specifying a protocol. For example, http://Server/[sites/]Web_Site/Lists/List_Title/AllItems.aspx.
Server-relative URL that is based on the server address and that begins with a forward slash, specifying a complete path from top-level Web site to file name. For example, /[sites/]Web_Site/Lists/List_Title/AllItems.aspx.
Web site-relative URL that is based on the address of a Web site object (SPWeb), that does not begin with a forward slash, and that specifies a complete path from the Web site's address to the file name. For example, Lists/List_Title/AllItems.aspx.
URL relative to a file or folder that is based on the folder containing the file that does not contain any forward slashes and that specifies the name of the file. For example, AllItems.aspx.
