15 amp (standard house type outlet): 1 hot, 1 neutral, 1 ground. Supplies up to 15 amps @ 120 VAC
30 amp RV: 1 hot, one neutral, one ground. Supplies up to 30 amps @ 120 VAC.
50 amp RV: 2 hots (240 VAC as measured between the two hots), one neutral, one ground. Supplies up to 100 amps @ 120 VAC (50 per hot). Just a with a stick and brick house, you could wire appliances to the two hots (240 VAC), but most all house appliances (exceptions are electric water heater, stove, oven, electric clothes dryer, A/C, etc-- the big stuff) AND MOST ALL RV appliances use only ONE HOT, so they are 120 VAC.