In photography, the diameter of the aperture expressed in terms of the focal length of the camera lens. The greater the f-number, the less light reaches the film and the more in focus the objects in the foreground and the background will be. For example, with an f-number = 16 the objects in the far background will be in focus. Whereas, with an fnumber = 2 the background will be blurry (while foreground objects are in focus).
— Computer Sciencerefers to the measurement of the opening in a camera lens that regulates the amount of light passing through and contacting the film.
— Film Terms