A keystone jack is a female connector used in data communications, particularly local area networks (LANs). The jack is usually mounted in a wall plate or patch panel. A keystone plug is the matching male connector, usually attached to the end of a cable or cord.
A principal advantage of keystone connectors is their versatility. Several types of keystone jack can be mounted on a single patch panel. They are available in unshielded and shielded forms, and can accommodate cords and cables having various numbers of conductors.