To add to what was said above, you may be thinking of a Green Slip, which is paid as single pay ‘above Reserve Guarantee’ for what is actually flown (no rotation guarantee on reserve, but 5:15 ADG and trip rigs still apply).

You also get payback days, which start 9 hours after release plus 24 hours for each day off interrupted (X-day/PB/TOFF). There is no limit, other than FAR limits, but you can’t get #2 until every other eligible pilot with a GS request in has turned down their first. It’s a way to balance GS across the seniority spectrum.