Counter-Strike Source is the trademark online multiplayer first person shooter from Valve software and Turtle Rock Studios. Other abbreviations for the title have been CS: Source or the even smaller CS:S. The title was initially available in 2004 alongside the release of Half-Life 2 however multiple disk and download versions have been available through Valve's proprietary online digital distribution system, Steam.
Counter-Strike matches consist of two teams, Terrorists and Counter Terrorists involved in several different match types. There are bomb maps and hostage maps. Bomb maps pit the terrorists against the counter terrorists by placing specific bomb sites in which the terrorists plant the bomb. Once the bomb is planted the counter terrorists have a set amount of time to defuse the bomb. If the bomb goes off or all of the counter terrorist players are killed the terrorists win the match. If the counter terrorists kill all of the terrorist players before the bomb is planted, Counter Terrorists win the round. Counter Terrorists can also win the round if the bomb is planted and then defused before the time limit is up.
Counter-Strike has had many modifications over the years. One of the most popular is a mod called GunGame. There are several iterations of GunGame but the most popular one is where all players start on a Glock pistol. Once a kill is made with that gun the player moves on up through the rest of the pistols. After a kill is made with all the pistol weapons the player will start using SMG (Sub Machine Gun) weapons followed by automatic rifles, sniper rifles, and finally the grenade and knife weapons. The first player to get a kill with all the weapons in the game is the winner.