The forward-firing phaser weapons of Defiant-class starships, which discharge rapid bolts of energy rather than a continuous beam and gave the small USS Defiant firepower far beyond its size.
Pulse phaser cannons fire short, intense bursts of phaser energy in quick succession. The Defiant class carries four of them facing forward, and the ship is flown almost like a fighter to bring them to bear.
They are introduced with the USS Defiant in the Deep Space Nine episode The Search, Part I, the ship having been designed originally to fight the Borg. The cannons are seen throughout the series, against the Jem'Hadar, the Klingons in The Way of the Warrior and Starfleet's own USS Lakota in Paradise Lost.
The same weapons are used by the Defiant against a Borg cube in the film Star Trek: First Contact, and by the cadet-crewed USS Valiant in the episode Valiant.