Canon EF 11-24mm F4L USM is an Auto Focus (AF) Wideangle Zoom lens with 35mm FF max sensor coverage. When mounted on a 35mm FF sensor camera, it will give you an FF equivalent focal range of 11 - 24mm. With a max aperture of f4 at 11mm, we can not consider this lens fast on wide end but f4 at 24mm is not too bad for tele end.
Canon EF 11-24mm F4L USM is weather sealed which makes it an ideal lens for outdoor use, especially when coupled with a weather sealed camera body.