Aperture-priority describes a metering method which recommends (or sets automatically) a shutter speed based on the aperture set by the user.

Given a choice of metering method, Aperture Priority may be chosen when control of depth-of-field is required. This may be either to ensure objects at different distances are in focus - by specifying a small aperture, or that some objects (perhaps the subject of a photo) are in focus whilst others (perhaps the background) are not - by specifying a large aperture.