Stands for the length of time a camera shutter is open to expose light into the camera sensor. If the shutter speed is fast , it can help freeze an action completely. If the shutter speed is slow , it can create an effect called motion blur where moving objects appear blurred along the direction of motion. This is useful to show movement and speed. A fast shutter speed means that the shutter is only open for a short period of time; a slow shutter speed means the shutter is open for longer.
This diagram shows the higher the shutter speed the easier it is to catch a clear picture whilst someone is running and the lower it is the picture will come out blurred.