Canon 800mm f5.6L IS USM is an Auto Focus (AF) Telephoto Prime 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 800mm. With the max aperture of only f5.6 at 800mm, it is considered a slow lens.
This lens features on optical image stabilization which helps capturing sharper images at lower shutter speeds. Canon 800mm f5.6L IS USM is weather sealed which makes it an ideal lens for outdoor use, especially when coupled with a weather sealed camera body.