In photography, the aperture refers to the opening in the lens that regulates the amount of light entering the camera. It is measured in f-stops, with lower f-stop values indicating a larger aperture size and more light entering the camera. Aperture also influences depth of field, determining how much of the image is in focus. A wide aperture (low f-stop) creates a shallow depth of field, ideal for portraits, while a narrow aperture (high f-stop) results in a deeper focus range, suitable for landscapes.