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 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.

Keystone modules have a rectangular face of 14.5 mm wide by 16.0 mm high and are held in place with flexible tabs. This allows them to be snapped into a mounting plate with correspondingly-sized rectangular holes, called ports. All keystones, regardless of the type of jack they carry, are interchangeable and replaceable. This provides much flexibility in arranging and mounting many different types of electrical jacks in one plate or panel without requiring customized manufacturing.