Ninja:

Ninja is a stealthy Counter-Strike 2 play in which a player plants the bomb, defuses the bomb, or otherwise completes an objective while staying hidden from the enemy team.

The term usually refers to a “ninja defuse,” where a player starts defusing in a position the defenders do not check, often behind cover, in smoke, or after a loud fight has pulled attention away. It matters because bombsite control in CS2 is as much about information as aim: if the opposing team loses track of the objective, a round can end even when they still have players alive. For example, after a site retake is delayed by smoke and gunfire, a player may slip onto the bomb and begin defusing before the remaining opponents realize it.

Related: Defuse, Bombsite (A/B Site), Retake, Clutch