Depth of field refers to the area of an image that appears sharp, and can be manipulated to achieve different visual effects. It is determined by the aperture, focal length, and focus distance of the camera. A wide aperture results in a shallow depth of field where parts of the frame are out of focus, while a narrow aperture creates a deep depth of field where the entire frame is in focus. Selective focus using a shallow depth of field draws attention to a specific area by keeping it sharp while blurring other parts of the frame.