What's called 'Universe Data Source' in Crystal Reports?
Universe Data Connection is for connecting Crystal Reports to a Universe type file(.unv), which are created by a Universe Design Tool by SAP. This file is an abstract layer between the db schema and the user. It gives an opportunity to do queries without knowing the underlying schema of the db, hence can be used by the staff who does not know SQL. 
In contrast Relational Connecting directs to a specific relational database. Both types can have only one connection.