Counter-Strike: Source, usually abbreviated as CS: S or CSS, is a video game developed by Valve Software. It is an evolution of Counter-Strike using the Source engine. As in the...original, Counter-Strike: Source stages a team of anti-terrorists against a team of terrorists in a series of rounds. Each round is won either by carrying out the mission (bomb explosion or hostage rescue) or by eliminating all members of the opposing team. Counter Strike: Source is one of the flagship games of electronic sport.