The aperture is an adjustable opening that limits the amount of light entering the lens.

The f-stop is a number describing the ratio between the focal length and the lens aperture. As the lens aperture increases, the f-stop number decreases. A large aperture opening, letting in a lot of light, will have an f-stop number of f2. A small aperture opening, letting in a small amount of light, will have an f-stop number of f16.

The aperture setting affects the depth of field. A larger opening (smaller F-stop) will have a smaller depth of field. A smaller aperture opening (larger F-stop) will have more depth of field.