It's a place on the internet that's not an MMO where people treat a video game like work.

Half of the players are government computer AI learning to kill humans.

I don't get it either fwiw.

I don't play this game either, but from what I understand, Valve likes to continually give players achievements to earn, which I imagine to be things like 'kill ten people in mid-air while screaming over voicechat'. These achievements and the rewards for completing them keep the game from getting stale, but instead of earning them in regular matches, some players create achievement servers hosting custom maps designed to make earning a particular achievement much easier than it would be during normal play.

This is a map that would presumably make earning some achievement easier if it weren't for the giant laser cat that eventually shows up.

THEY'RE IN MY EYES AUUUUGGHHHHH