Counter-Terrorists in Counter-Strike 1.6 and Counter-Strike: Source are the opposing force of terrorists, counter-terrorists goals are to eliminate the terrorists and/or defuse a bomb (C4) which is planted in one of two bombsites, named Site A and Site B, maps which contain the bomb plant/defuse scenario are named accordingly, beginning with the suffix de_, examples of such maps include de_dust, de_dust2, de_inferno, de_nuke and many more. Although plant/defuse is the main scenario there is another mode which is hostage rescue, the goal for the terrorist side is to maintain control of the hostages and the goal for the counter-terrorists is to either kill all terrorists or lead the hostages back to the counter-terrorist spawn-point.
Counter-terrorists have 4 different classes to choose from, though the only difference between each class is aesthetic - the classes are as followed (taken from in-game)
Seal Team 6
ST-6 (to be known later as DEVGRU) was founded in 1980 under the command of Lieutenant-Commander Richard Marcincko. ST-6 was placed on permanent alert to respond to terrorist attacks against American targets worldwide.
GSG-9 was born out of tragic events that led to the death of several Israeli athletes during the 1972 Olympic games in Munich, Germany.
The world-renowned British SAS was founded in the Second World War by a man named David Stirling. Their role during WW2 involved gathering intelligence behind enemy lines and executing sabotage strikes and assassinations against key targets.
France's elite Counter-Terrorist unite, the GIGN was designed to be a fast response force that could decisively react to any large-scale terrorist incident. Consisting of no more than 100 men, the GIGN has earned its reputation through a history of successful ops.