There's two types of reserve: Long Call and Short Call. Long Call is a 12 hour call out and Short Call is a 2 hour call out.
There is ready reserve (they call it ARC...Airport Reserve Crew or something like that), but you can only be assigned it 6 times in a bid period and you can't be assigned it two days in a row or on you last day unless you waive those rules. Also you can't be junior manned to sit ARC. They are 4 hour sits and you get 4 hours of credit for doing it.
I'm on reserve in CLE, but hopefully I'll be holding a relief line in the next couple months. I was hired May of 2011.