Shutter speed refers to the length of time a camera's shutter remains open to allow light to hit the camera 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 capturing motion or low-light scenes. Adjusting the shutter speed affects the exposure of an image. A faster shutter speed lets in less light, resulting in a darker image, while a slower shutter speed allows more light, leading to a brighter image. Balancing shutter speed with aperture and ISO is essential for achieving the desired photographic effect.