In Star Trek: The Original Series, the handheld weapon that fires adjustable energy beams is the phaser.
Phasers are directed-energy weapons used throughout Star Trek by Starfleet personnel and many other groups. Their settings can produce different effects, including stunning, killing, and cutting or heating solid matter. The name is commonly expanded as “photon maser,” although the franchise usually presents “phaser” as the standard term.
The original television series showed hand phasers and larger rifle-like phaser weapons. Later Star Trek productions redesigned their shapes, but retained the basic idea of a weapon with selectable power settings. Phasers are often confused with photon torpedoes, which are explosive projectile weapons launched by starships, or disruptors, which are energy weapons associated especially with Klingon and Romulan forces.
The phaser became one of Star Trek’s most recognizable fictional technologies because it serves several roles: personal defense, shipboard combat, industrial cutting, and controlled destruction of objects.