A directed energy weapon was a device which, in the form of a gun or other type of weapon, fired a beam, pulse, or projectile made of, or charged with, high-energy particles or other energies. Most spacefaring species had the technology to fire directed energy, as it was preferable to firing projectile weapons in pressurized environments, and more effective against shielded components or personnel.
There were a wide array of methods available for dispensing such a discharge, from plasma weapons, lasers, and phase weapons to Starfleet's phaser weapons, which fired particles called nadions. Another common energy discharge weapon was the disruptor, used by Klingons and Romulans. Compressed tetryon beam weapons were used by other Alpha Quadrant civilizations. (TOS; TNG; DS9; ENT)
Subspace weapons of directed energy, including isolytic bursts, were generally forbidden by treaties, such as the Khitomer Accords. (Star Trek: Insurrection)
Advanced weapons existed, in the forms of the planet-destroying antiproton beam mounted on the so-called "planet killer". Federation technology had very little to match this technology when faced with one such weapon in 2267. (TOS: "The Doomsday Machine") The Xindi superweapon was another planet-killer utilizing a directed-energy beam, but it was destroyed before the Sphere Builders, manipulating the Xindi, had an opportunity to complete their plan by using the device on Earth. (ENT: "The Expanse"; ENT Season 3)
The Ennis, a Gamma Quadrant species, stopped using directed energy centuries before 2369, as it was, in Golin Shel-la's words, "not damaging enough". (DS9: "Battle Lines") A directed-energy weapon (DEW) emits energy in an aimed direction without the means of a projectile. It transfers energy to a target for a desired effect. Intended effects on humans may be non-lethal or lethal. These effects have been categorised as physical, physiological and psychological.[1] The technology has been available for several decades in the United States Department of Energy National Laboratories,[2] NATO and Czech Ministry of Defence.[3] Currently, the technology is being considered for non-military use to protect Earth from asteroids.[4]
The energy can come in various forms:
Electromagnetic radiation, in lasers or masers
Particles with mass, in particle-beam weapons (technically a form of micro-projectile weapon)
Sound, in sonic weapons
In science fiction, these weapons are sometimes known as death rays or rayguns and are usually portrayed as projecting energy at a person or object to kill or destroy. Many modern examples of science fiction have more specific names for directed-energy weapons, due to research advances. Flamethrowers do not fall into this category, because they are actually projectile weapons; the projectile (gas or liquid) is simply on fire.