A lens hood is a device used on the end of a lens to block the sun or other light source in order to prevent glare and lens flare. They are also useful for protecting the front element of your lens for any potential damage and scratching.
Lens hoods are more prominent in telephoto lenses because the field of view has a smaller viewing angle than of wide-angle lenses. For wide angle lenses, the length of the hood (away from the end of the lens) cannot be as long as those for telephoto lenses because of the viewing angle.
Compatible with the following Canon lenses: