What is "ballistic knife"

n. A weapon that fires a knife blade.

A ballistic knife is a knife with a detachable blade that can be ejected to a distance of several yards by pressing a trigger or operating a lever or switch on the handle. Spring-powered ballistic knives briefly gained notoriety in the United States in the mid-1980s after commercial examples were marketed and sold in the United States and other Western countries. Since then, the marketing and sale of ballistic knives to civilians has been restricted or prohibited by law in several countries.