Telephoto Lens
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 lens in which you adjust the focal length over a wide range.
A 50mm lens with a 3x zoom is the same as a lens having the capability to go from 50mm to 150mm.
In effect, this gives you lenses of many focal lengths.