Photographic exposure refers to the amount of light that reaches the camera's sensor or film during a photograph. It is determined by three main factors: aperture, shutter speed, and ISO. The aperture controls the size of the lens opening, the shutter speed determines how long the sensor is exposed to light, and the ISO setting adjusts the sensor's sensitivity to light. Proper exposure is crucial for capturing images with the desired brightness and detail. Underexposed images may appear too dark, while overexposed images can lose detail in bright areas. Photographers often use exposure meters to help achieve the correct balance for their shots.