What is a slide stop on a gun?

A slide stop is a mechanism found on semi-automatic guns that holds the slide in the open or locked back position when the gun is empty or the shooter desires to disengage the slide. It is usually located on the frame of the gun and can be activated by either pressing a button or pulling down a lever. The slide stop serves as a safety feature to prevent the gun from firing when there is no ammunition in the chamber and also allows for easy reloading of the gun.