What does the slang word shank mean?

A shank is a homemade knife or similar weapon, usually made on the streets or in prison. An inmate may break the handle off of a plastic fork and sharpen one end of it. If they can find a piece of metal, perhaps smuggled out of a metal shop, they may grind it to a point or sharpen it on at least one edge. They might even put tape around it or fasten it to a stick. In one jail, someone had managed to remove a piece of molding from the wall and make a crude sWord out of it.