Sigma 18-125mm F3.8-5.6 DC OS HSM is an Auto Focus (AF) SuperZoom 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 27 - 187.5mm. With a max aperture of f3.8 at 18mm, we can not consider this lens fast on wide end and neither at tele end with its f5.6.
This lens features on optical image stabilization which helps capturing sharper images at lower shutter speeds. Sigma 18-125mm F3.8-5.6 DC OS HSM is not a weather sealed lens, so you have to be extra careful against rain and dust.