In “The Corbomite Maneuver,” Kirk invents corbomite as a bluff. He claims that the Enterprise carries this fictional substance and that any attacker would be destroyed by a powerful defensive reaction.
Kirk uses the story when the Enterprise is confronted by Balok, commander of the enormous Fesarius. After Balok threatens to destroy the ship, Kirk argues that attacking the Enterprise would be dangerous even for a vastly superior vessel. The claim is entirely improvised; corbomite is not an established Federation material.
The bluff helps Kirk buy time and also reveals his willingness to use psychology instead of force. The apparent threat eventually leads to a surprising first-contact encounter: Balok is testing the Enterprise crew, and his frightening image is only an effigy. The episode originally aired on November 10, 1966, as the tenth broadcast episode of the first season.
A common mix-up is confusing corbomite with real or recurring Star Trek substances such as dilithium, pergium, or tritanium. Kirk later reuses the corbomite bluff against Romulans in “The Deadly Years.”