In the xTuple environment there are users and user accounts. Users refers to the log in required to access the xTuple postgres database cluster. Once inside the database cluster, you may access the database(s) established for your organization. There may be multiple databases in a cluster.
User accounts are defined on a per database basis. For example, let's say you want to give someone access to your production database but not the pilot database—because special testing is being performed there. In this case, you would create a user account for them in the production database but not in the pilot.
Users can access only databases where they also have a user account.