When you are cladding any surface with brick slips you may have external 90 degree angles on the project such as a return around or a wall or window reveal and even on the outside of a fire place, brick slip corners also know as corner pistols allow you to complete a professional and tidy finish that will look like full size conventional bricks have been used.
Generally when you use a corner slip it will be identical in colour, shape, texture and size of flats pieces although some builders and tilers will add character to a wall by using a contrasting brick such a red flat slip with a cream or grey corner pistol. They are also used for making arches over doorways and above inglenook fireplaces as they are light in weight and can go around curves quite easily.