In Counter-Strike bomb-defusal mode, what device do terrorists plant?

In Counter-Strike bomb-defusal mode, terrorists plant the C4 explosive.

At the start of a bomb round, one terrorist carries the bomb, commonly called the C4. The terrorist team wins by planting it at one of the map’s bomb sites and protecting it until the timer expires, or by eliminating the entire counter-terrorist team before the round ends.

Counter-terrorists can win by eliminating the terrorists, preventing the plant, or defusing the bomb after it has been planted. A defuse kit shortens the required defuse time in versions that use that equipment. The bomb objective gives each team a distinct tactical role beyond simple elimination.

The C4 name refers to a real plastic explosive designation, but the game’s device and timer are fictional gameplay abstractions. Players may also call it the bomb, so “C4” and “the bomb” usually identify the same objective item in this mode.