So there are three FAA recognized reserve types. Long call = more than 10 hour notice and on call pretty much 24 hrs a day on your work days. Short call/RAP (reserve availability period). About a 14-16 time frame you are legal to work. 1.5-3 hour call outs for companies is standard with 2 hrs being the most used. (Envoy uses a 3 hr call out for LGA and 2 for all other bases)
Airport standby- You are considered on duty and can fly what ever the FAA says you are legal. Usually you go home after 8 hours of no call.

Everything that's been said here is pretty much spot on. But like AZFlyer said it all depends on company staffing. I got raked over the coals in October but Nov. and Dec were a cake walk. So it's dynamic from month to month or year to year.

Sometimes I have to take separate cars to things with the family on the off chance I get called. I typically know when I will get called based on open flights and reserves available, however sometimes I get surprised by the call or no call.

Reserve time at all airlines are low due to hiring. It looks like you want to get off reserve ASAP and want to fly. Good luck.