Shutter speed refers to the length of time a camera's shutter remains open to allow light to hit the image sensor. It is measured in seconds or fractions of a second, such as 1/1000 or 1 second. A fast shutter speed captures quick movements clearly, while a slow shutter speed can create a blur effect, making it useful for artistic shots or low-light conditions. Adjusting the shutter speed affects the exposure of a photograph. A faster shutter speed reduces the amount of light entering the camera, resulting in a darker image, while a slower shutter speed increases light exposure, leading to a brighter image.