The shutter speed determines the amount of time the camera's sensor is exposed to light. It is measured in seconds or fractions of a second, such as 1/1000s, 1/250s, 1/30s, etc. Fast shutter speeds (e.g., 1/1000 or more) freezes fast-moving subjects and reduces motion blur, while a slow shutter speed (e.g., 1/30 or less) allows more light and can capture motion blur.