30 Amp Confusion

Hi, I'm a new RVer and have a question about an older (1989) motorhome. When I open the panel where my 30 amp electric cord is located there is a very short cord (about a foot) with a 30 amp male plug which I assume you would plug a 30amp extension cord into it to reach the campground receptacle . Connected to this is a receptacle with a female outlet. From there the cord runs to the fuse box. My question is this...what is the square boxed receptacle with the female plug-in? Is this just an extra place to plug a 30 amp cord into or is there some other purpose?
Sorry if I have all the terminology wrong. :) Thanks!!!