A Stunner is a general term for a science fiction weapon that is designed to temporarily impair the motor and/or cognitive functions of a living being, usually by rendering it unconscious, but otherwise unharmed.
The most famous examples of this kind of weapon include:
Phasers in the Star Trek franchise which can be set to stun an opponent with variable severity.
Stunners in the Vorkosigan Saga by Lois McMaster Bujold which causes a temporary reduction in nerve activity within a radius of the impact site.
Stunners in the Solar Queen series by Andre Norton which disrupt the motor function, although leaving the shot person conscious.
The Wraith of Stargate Atlantis use stunners to capture humans alive, in order to feed on their life energy.
Also in Stargate Atlantis, Ronon Dex's personal energy pistol can be set to two settings: stun and kill.
Stargate SG-1's Zats are not true stunners; although one shot is sufficient to stun, a second burst is fatal. The single shot from a Zat does not necessarily incapacitate, as strong or prepared enough targets can shrug off the effects in several seconds (the second shot is still fatal).
In Battlefield Earth, Psychlo weapons are basically two-in-one, with one barrel firing destructive shots and the other emitting green pulse that stuns and knocks the target back.
In the novel Dune stunners are projectile weapons whose pellets knock out their targets.
