An application release is a release of application data. It is the combination of a production version of a repository with an id. This id can be any number or code, up to 8 characters long. As a suggestion, you could use any of the following:
appdata, app01, tours, APPTODAY, 20100427.
Application releases are exported in XML format. They are stored in the Applications folder, as specified in the Folder Locations window, for example:
C:\XML Repository Manager\applications\