Bomb defusal (de) is a game mode where the main objective for the Counter-Terrorists is to prevent the Terrorists from planting the C4 explosive. Counter-Terrorists can win the round by defusing the bomb, while the Terrorists must plant the bomb at one of two bombsites (usually located near Counter-Terrorist spawn) and ensure detonation of the explosive. The secondary objective, which also secures a victory for either team, is to eliminate all members of the opposing team (however, if the bomb is already planted and all Terrorists are eliminated the round does not end until the bomb is defused or detonated). If the round time expires, the Counter-Terrorists win by default.
The bomb can only be planted at a bombsite, of which there are two on every official map. Counter-Terrorists may purchase a defusal kit that decreases the time needed to defuse a bomb.
Bomb defusal is by far the most popular and most balanced game mode. For those reasons, it is usually the only game mode used for tournaments or other competitive matches.
In the sound files of Counter-Strike, there are details about Bombsite C. However, no official map uses more than 2 Bomb sites (although there was a beta map that contained three bombsites). In addition, bots in Counter-Strike: Condition Zero and Counter-Strike: Source have unused quotes mentioning a bombsite C (examples include "The bomb is ticking at (bombsite) C" and "(The) bomb's at (bombsite) C").