A prime lens is a lens with a fixed focal length, as opposed to a zoom lens which has an adjustable focal length. Prime lenses typically take higher quality photos and video because the optics can be fine tuned for an exact focal length. On a zoom lens a range of focal lengths have to be accommodated and the glass can only be shaped perfectly for one level of magnification. Typically when a zoom lens is at either of its extremes some undesirable perspective distortion occurs. Another plus is that prime lenses are more durable because they have fewer moving parts. Prime lenses are typically more affordable, faster (accommodate larger apertures to let light in faster), and higher quality.