A blade is the sharp, cutting portion of a tool, weapon, or machine, specifically designed to puncture, chop, slice, or scrape surfaces or materials. Blades are typically made from materials that are harder than those they are intended to cut. This includes early examples made from flaked stones like flint or obsidian, evolving through the ages into metal forms like copper, bronze, and iron, and culminating in modern versions made from steel or ceramics. Serving as one of humanity's oldest tools, blades continue to have wide-ranging applications, including in combat, cooking, and various other everyday and specialized tasks.

A ballistic knife is a knife with a detachable blade that can be ejected to a distance of several meters/yards by pressing a trigger or operating a lever or switch on the handle. Spring-powered ballistic knives first appeared in books and press reports on Soviet and Eastern Bloc armed forces in the late 1970s. Commercially-produced ballistic knives briefly gained notoriety in the United States in the mid-1980s after they 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 nations.