The photon torpedo is the standard heavy projectile of Starfleet vessels, a casing carrying a matter-antimatter warhead launched from tubes and capable of travelling at warp speed.
Photon torpedoes have been the primary heavy weapon of Federation starships since the 23rd century. Each consists of a self-propelled casing holding a small quantity of matter and antimatter kept apart until detonation, when their annihilation releases enormous energy. They can be fired in single shots or spreads and their yield can be adjusted.
The torpedoes have uses beyond combat. Their casings have been adapted as probes, as containers, and most memorably as the coffin in which Spock was laid to rest after his death aboard the Enterprise in 2285, the casing later coming to rest on the Genesis planet.
The weapon was a staple of the Klingon conflicts of the 23rd century and remained in service into the 24th and beyond, though more powerful quantum torpedoes were introduced on frontline ships such as the Defiant. Earlier Earth ships used spatial and photonic torpedoes as predecessors.