A referal can be as detailed as you and T decide.

Some referrals that I receive from other T's include a name/number (with release) of the client that's being referred. Some are more indepth, like an entire intake, with historical information so the client doesn't have to repeat that process. Others are summaries of treatment progress, diagnostic information, etc.

As a client, referrals I've gotten were just a name and number of another T for me to call.