A six-shooter is a small handgun that holds six bullets, of the kind you see in old American Westerns. The bullets sit in a turning cylinder; after each shot the cylinder moves on, so you can fire six times before you reload. Cowboys, sheriffs, and film outlaws carry them — dusty streets, swinging doors, that whole picture. In real history it was a revolver, used in the late 1800s on the American frontier. Today almost nobody uses the word for a modern pistol; it belongs to stories, films, museums, and playful talk. It is informal and a little old-fashioned. The gun is “small” next to a rifle, but it is still a real firearm, not a toy. People sometimes stretch the word for any old revolver, even if it holds a different number of rounds, but the name itself is built on those six shots.