F.A.U. and W.A. abbreviations on circuit breaker?

If you have a outside compressor this requires a separate circuit than the air handler or forced air unit. Wa to me would be water if you have a well. The double 50 is most often for an electric range.

FAU = Forced Air Unit (another name for an air handler)

A FAU is a Forced Air Unit, which is another name for an air handler, indoor unit, or AHU for short. Whatever you call it, it consists of a blower, air conditioning coils, and sometimes electric heat strips or a hydronic coil, all wrapped up in a furnace-shaped package. (It doesn't have a gas or oil burner in it, though, which is what distinguishes it from a furnace.)

The separate breaker labeled AC, then, turns off the outdoor (condensing) unit for your air conditioning or heat pump. They are on separate breakers so that an issue with the air conditioning doesn't knock out the indoor unit and its air-circulating functions, or worse yet, your heat if you have a hydronic coil in your forced air unit.

W.A. is likely your kitchen receptacle circuits

While I don't know what W.A. stands for precisely, from a process of elimination, we can deduce that those breakers likely feed your kitchen small appliance branch circuits, as the NEC requires at least two 20A circuits dedicated to the kitchen countertop receptacles.