roughly...
737 has 3 hyd systems: A,B and a sby which can be switched on manually.
each A/B has one eng driven hyd pump and one elec driven powered by the other engine's generator.
A system has gear, altn brake, flaps, flt cont, half the spoliers, rev, one AP
B has brake, alternate gear, flt cont, rev, half the spoilers, the other AP
so the "A" pumps are the pumps powering/pressuring system A ..... and on the "classics" they are switched off for push-back to prevent damage to the nose-gear......