The TFS Data Tier is composed of 13 SQL Server databases as follows:
2 Reporting Services and 4 WSS databases: ReportServer, ReportServerTempDB, WSS_AdminContent, WSS_Config, WSS_Content, WSS_Search
7 TFS-specific databases: TFS Databases: TfsActivityLogging, TfsBuild, TfsIntegration, TfsVersionControl, TfsWarehouse, TfsWorkItemTracking, TfsWorkItemTrackingAttachments
You can learn more about each one of these at http://msdn.microsoft.com/en-us/library/ms253070.aspx or by googling them. In my Firefox browser I select the word I want to google in the browser, right-click and then select "google ...." from the menu.