Site Directory in SharePoint Server 2010
SharePoint Portal Server 2003 and Office SharePoint Server 2007 provided a Site Directory that was commonly used to “catalog” the collection of sites within a server farm environment, most commonly, organizations used categories to isolate like or related site collections and the built-in provisioning callback to ensure site collections were listed in the Site Directory on creation.
https://blogs.technet.com/wbaer/archive/2010/04/29/site-directory-in-sharepoint-server-2010.aspx