Wiktionary
n. (context video games English) A device resembling a gun that allows the player of a video game to target a point on the screen.
Wikipedia
A light gun is a pointing device for computers and a control device for arcade and video games, shaped as a pistol.
Modern screen-based light guns work by building an optical sensor into the gun, which receives its input from the light emitted by on-screen target(s). The first device of this type, the light pen, was used on the MIT Whirlwind computer.
The light gun and its ancestor the light pen are now rarely used as pointing devices due largely to the popularity of the mouse and changes in monitor display technology—conventional light guns only work with CRT monitors.
Usage examples of "light gun".
A plop of sound accompanied it, not unlike the setting off of a photographer's flash light gun.
Even in the tricky light Gun Moll recognized the dark object that Sin Lo held up before his snarling face.
Oh, I note controls for a coherent light gun but that wouldn't be much use to a pirate.
Two men down in the confusion around the light gun, and then his troopers were past.