Belows lists the default databases
Contains archived objects. Sitecore can be configured to automatically remove objects from the Master database to the Archive database on a specific date. This removes old objects from the Master database but backs up a copy of the object. You can specify the archive date in the Content Editor » Tasks » Archive Date field.
Contains the Sitecore client.
Contains the extranet security settings.
Contains the site under development.
Contains deleted objects. Items can be restored via the Sitecore » Administrator Tools » Recycle Bin application
Contains the client security settings.
Contains the published web site.