Alternatively known as exposure time, shutter speed is a camera specification that defines the period over which a camera is collecting data for an image. For example, a shutter speed set to 1/60 takes 1/60th of a second for the necessary light to enter the lens to capture an image. If the shutter speed is longer, more time is condensed into a single photograph, allowing the motion to become more noticeable. Shutter speed is an adjustable setting on most modern digital cameras.
In the image, the long shutter speed example shows a higher range of motion, because the image was taken over the course of a few seconds rather than a fraction of one.