Canon 75-300mm f4.0-5.6 III is an Auto Focus (AF) Telephoto 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 75 - 300mm. With a max aperture of f4 at 75mm, we can not consider this lens fast on wide end and neither at tele end with its f5.6.
Canon 75-300mm f4.0-5.6 III is not a weather sealed lens, so you have to be extra careful against rain and dust.