An imaginary material that James T. Kirk claimed was built into the hull of the Enterprise, said to reflect any destructive energy back upon an attacker, and used purely as a bluff.
Corbomite does not exist. It is a fiction devised by Captain Kirk in 2266, in the episode The Corbomite Maneuver, when the enormous alien vessel Fesarius and its commander Balok announce that the Enterprise will be destroyed. Inspired by Spock's comparison of the stand-off to chess and McCoy's talk of bluffing, Kirk turns to poker instead.
He tells Balok that every Starfleet ship carries corbomite, a substance that returns any attack with equal force and destroys the aggressor. Balok hesitates, and the countdown passes without incident.
Kirk reuses the trick in The Deadly Years, broadcasting in a code he knows the Romulans have broken that he is about to trigger a corbomite device, which sends the surrounding Romulan ships into retreat.