What the fuck does CT mean?? My teammates kept screaming at me "hes CT, hes CT!" and then thought I was trolling when I didnt know what that was ("Bro we told u he was fucking CT, and ur looking the other way!")

When I pull up my map, I dont see any places named CT, so it cant be a place on the map - as their language would suggest. Is it some kind of ability or buff that the enemy has?

Please help, so confused.