A lens with a long focal length, generally above 55mm, which enables a distant setting to be brought closer than a standard lens would allow for photographing.
A 50mm lens with a 3x zoom is the same as a lens having the capability to go from 50mm to 150mm.
A lens that makes a subject appear larger on film than does a normal lens at the same camera-to-subject distance.
A telephoto lens has a longer focal length and narrower field of view than a normal lens.