The shutter is a curtain in front of the sensor. It determines HOW LONG the camera sensor is exposed to light for. Shutter speeds are measured as seconds or fractions of a second as stops of light and are described as FAST or SLOW. For example 1/125th or one hundred and twenty fifth of a second is a FAST shutter speed, 2″ or two seconds is a SLOW shutter speed.
1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1”, 2”, 4″
Shutter Speed controls the length of time the sensor is exposed to light for. It also controls whether movement is frozen or blurred. A fast or high shutter speed freezes motion, a slow or long shutter speed causes motion blur.