Pentax 21mm F3.2 AL L is an Auto Focus (AF) Wideangle Prime lens with APS-C / DX max sensor coverage. When mounted on a APS-C / DX sensor camera, it will give you an FF equivalent focal range of 31.5mm. With a max aperture of f3.2 at 21mm, this is a moderately fast lens.
Pentax 21mm F3.2 AL L is not a weather sealed lens, so you have to be extra careful against rain and dust.