The term "f/4" refers to an aperture setting in photography, indicating the size of the lens opening. A lower f-number, like f/4, means a larger opening, allowing more light to enter the camera. This can result in brighter images and a shallower depth of field, which helps to blur the background and emphasize the subject. Aperture settings are part of the exposure triangle, which also includes shutter speed and ISO. Understanding f/4 is essential for photographers aiming to control light and achieve specific artistic effects in their images.