Use Connection to specify an AnyDAC connection object to use to connect to an DBMS. 

At design-time, select from the list of available TADCustomConnection objects (if any have been added to the application) invoked from the Object Inspector. If a form or data module has TADCustomConnection dropped on it, then TADRdbmsDataSet assigns this connection object to Connection property automatically right after dropping on the form or data module. 

At runtime, set Connection to reference an existing TADConnection object. 

The TADRdbmsDataSet can be bind to TADCustomConnection object using Connection or ConnectionName property. Using ConnectionName property allows to bind to a connection object, if it is even not yet created or is not accessible.

property Connection: TADCustomConnection;

ConnectionName