The 110v plug is for whatever you want to plug into it. I use it to plug an incandescent light bulb in during the rare times we are under a hard freeze warning down here as I never winterize.
The idea about it being an inverter feed is a possibility but unlikely unless an owner wired it that way. I'm thinking of running an extension cord from our battery bank back to the power bay and tying a cheap little 800w inverter I have had forever. That way, I could run the fridge on electric while driving and kids can plug their chargers in anywhere when underway.