Beam setting
A beam setting was the amount of discharge given-off by a directed energy weapon, such as phase-pistols, plasma rifles, phasers, or disruptors. It was similar in concept to the variable yield capability used on torpedoes. 

When Spock, Data, and Jean-Luc Picard outmaneuvered Sela in her office, Spock held a captured Romulan disruptor to her and warned her "I'm afraid I don't know too much about Romulan disruptor settings," forcing her to surrender. ()

Stun setting 

The stun setting was non-lethal, low yield beam setting; powerful enough to cause disorientation, unconsciousness, and minor skin burns to a humanoid lifeform. (; ; ) While relatively benign to a humanoid, some stun settings could cause smoke, sparks, electromagnetic discharge, or any combination of the above to be emitted from walls and other solid surfaces and objects the beam struck. (; )

Romulan disruptors had no stun setting, and nor did at least some 22nd century Andorian weapons. (; )

There were many resilient species against which the stun setting had little or no effect, including Augments, () the Xindi-Reptilians, () and Humans infected by a parasitic being. () Angosians who had undergone conditioning to fight in the Tarsian War were also largely unaffected by the stun setting. () To some more vulnerable species, even the stun setting was potentially lethal, for example the Trill symbionts. () When used at close range, a phaser set on stun was capable of inducing sufficient trauma to kill a Human, if fired at a vital organ such as the brain. ()

Phase-pistols in use by Starfleet in the 2150s featured stun as one of two settings, the other being kill. () Their stun setting could also be used to ignite fires. () Later Starfleet phasers in the 23rd and 24th centuries had several different levels of stun setting. Starfleet regulations stated that phasers were to be locked at the level one stun setting. ()

A phaser set to stun could render a Human female unconscious in 0.9 seconds, something that was of no use to Miles O'Brien when a Pah-wraith possessed his wife, as it was still more than enough time for the Pah-wraith to kill her. ()

Levels of stun
 The first stun setting was called the "low stun setting", () "setting number one" and the "base cycle". () A hit from this most minimal setting only left the target dazed, unable to stand and think straight for a short time. (, ) Two phasers set on setting one, fired simultaneously, could break large objects into pieces, such as the urns of the second planet of the Taurean system. () In the 2290s, a phaser fired on stun did not set off internal alarms on Starfleet starships. ()

 A higher stun setting caused a brief moment of unconsciousness to most humanoids. Although mostly harmless when used at this setting, multiple phaser stuns like this could culminate in serious injury to the central nervous system, and, after multiple hits, death. ()

 The highest stun setting had several names. It was referred to as "maximum stun", () "full stun", () "heavy stun", (; ) "heavy stun force", () and "strong stun position". () The highest stun setting was strong enough to immobilize a Soong-type android. () The slightly higher setting 3.1 was also enough to cause a Changeling to experience similar discomfort as the minimal setting caused to Humans. Setting 3.4 or 3.5 was high enough to effectively stun and force a Changeling to revert back into its gelatinous state. ()

Modifications
In a similar way as the kill setting could be used to quickly kill a room full of people when set on a wide beam setting (), a wide-field stun setting could be used to stun large groups with a single shot. (; )

Along with hand weapons, shipboard phaser banks could be modified to deliver a potent stunning beam to incapacitate large crowds on the surface of a planet, when fired from orbit. ()

Kill setting 

The kill setting was a yield setting that was intended to cause death to a humanoid lifeform. (; ) 

On a type 2 phaser used by the Starfleet in the 23rd century, "one-quarter" and "force 3" were other terms for the kill setting. In the 24th century, the setting was known as "level 10". (; )

Yield
On phase-pistols used by Starfleet personnel in the mid-22nd century, the kill setting was the normal maximum setting, and was rated at a yield of five megajoules. ()

Cardassian phase-disruptor rifles were also similarly designed with only two settings and the maximum yield of 4.7 megajoules. ()

The impact of a phaser or a disruptor blast set to kill left behind an electrostatic charge. () A phaser set to kill also left behind a distinct phaser burn on clothing. In 2370, Jason Vigo suggested to Bok that he could create such a phaser burn on his shirt and send it to Captain Jean-Luc Picard, to try to convince him that Bok had killed him. ()

Applications 

Andorian rifles used by the Andorian Imperial Guard in the mid-22nd century were set to kill by default; they had no stun setting. ()

When a phase-pistol set to kill only grazed a target, it was possible to survive from the hit. ()

In 2267, the kill setting was found to be non-lethal to the flying parasites that invaded Deneva. Because each parasite was part of a huge organism, and drew strength from that organism, it could resist extended exposure to a hand phaser set to kill. Parasites exposed for five to ten seconds reacted as if mildly stunned; they fell from the surface to which they were attached, and did not react to external stimuli for about a minute. ()

The kill setting on hand phasers used by the Mordanites in 2364 had a distinct sound from the stun setting. ()

To a Human infected by a parasitic beings, the kill setting only caused unconsciousness, due to the high levels of adrenaline stimulated by the parasite. However, extended exposure to a body part such as the head of a humanoid would still cause it to explosively vaporize. Two phasers set to kill could also vaporize smaller lifeforms such as the neural parasite mother creature with extended exposure. ()

In 2366, Commander William T. Riker of the  was forced to use his phaser to disintegrate the Acamarian servant girl Yuta to prevent her from killing the Lornak tribe leader Chorgan. Stun and kill settings only caused her to recoil in pain due to her genetic enhancements. ()

See also
 Neural truncheon
 Stun baton
 Stun grenade
 Stunstick

Measurements
Directed energy weapons