A covariant phaser pulse was a specialized directed-energy discharge capable of taking advantage of phase retractions in an enemy vessel's shield configuration.
In 2372, while engaged in combat with a Reptohumanoid vessel in the Delta Quadrant, Lieutenant Tuvok, chief tactical officer of the USS Voyager, detected a slight phase retraction in the shields of the enemy vessel, whenever the enemy transferred auxiliary power to their aft weapons systems. Utilizing a covariant phaser pulse fired at the enemy vessel's aft control systems, Tuvok was able to disable their entire weapons array. (VOY: "Parturition")