The aperture is the size of the opening in the camera's lens that allows light to enter. Aperture is also often referred to as the f-stop and is typically denoted as f/1.4, f/2.8, f/5.6 etc., with lower numbers representing larger openings and allowing more light to come in. A wide aperture (e.g., f/1.4) lets in more light and results in a shallow depth of field. A narrow aperture (e.g., f/16) allows less light and results in deep depth of field, keeping more of the background in focus.