A compensator.

Elo, used in Chess games... as for now people use that term for many other things.

I'll give you a proper answer. It's a rating system that was (I believe) originally used in games such as chess to determine player skill. It's a fairly common system that has been widely adapted into many games. Games such as clash of clans/clash Royale (the trophies) use a similar system, and is used in destiny as a third party rating. Basically it's a number, and when you beat people, it goes up and when you lose it goes down. How much it goes up/down is dependant on how much Elo the other players have. If you beat people who have significantly less Elo than you, it will barely increase. It's also non destructive, in the way that your history on the game won't effect your ability to change it, unlike KD where you will have a hard time increasing it if your KD used to be terrible. The main site for seeing it is guardian.gg, my Elo used to be reasonably high (around top 1000) but right before and after the season reset I stopped caring and playing, so my Elo this season is pretty much terrible.

A band.

It's a team/win based score. Shit team= shit Elo! Unless you can dbl carry!

The thing kids with worst stats than yours use to make them fell good.

The higher your elo the smaller your manbits are.