What does this mean?

From the ungodly, perverted vivisection on the Island of Dr. Moreau, could it be a balanced interconnect reterminated with RCA plugs?

ah Jameswei! You may have it!
I'll take a set.

Or, do you take the extra wire and plug it into the wall receptacle?

It simply means that one end of the cable weighs the same as the other end. If you coil it up and heave it into the woods, it will spiral gracefully into the void. Which is probably what you should do with such a confused cable. :-)
I'd try another seller, myself.
Still unbalanced,
Ed

Euro balanced interfaces sometimes use RCA's; 1 cable for inverting & another cable for non-inverting. Take a look at an Electrocompaniet component for an example of this approach.

This simply means that the cable has three conductors inside even though it has RCA's on the end. It has two conductors and a shield. The cable can easily be made fully balanced by replacing the RCA's with XLR's. All one has to do is solder the red wire to pin two the black wire to pin three and the shield to pin one. Or, for Europeans use the black wire for pin two and the red wire for pin three.