What is the Elo rating?

It's a way to give a single number to your skill set. And this is based on kills, deaths, time played. There's a formula, actually. If you check Wikipedia, I think it's just a formula. But again, I'm not really that involved in that side of it. But I looked it up because I asked everybody one time, what does ELO stand for? I thought it was an acronym. And nobody had the answer, but Google did.