Aperture in photography refers to the opening within a lens through which light passes to enter the camera. It is measured in f-stops and plays a crucial role in controlling the amount of light that reaches the camera sensor. The aperture also influences the depth of field in an image, determining how much of the scene is in focus. A smaller aperture (higher f-stop number) results in greater depth of field, while a larger aperture (lower f-stop number) creates a shallower depth of field with a blurred background. Understanding how to manipulate the aperture is essential for creating visually appealing photographs with varying degrees of sharpness and background blur.