Network interface device

Not to be confused with Network Device Interface or Network interface controller.
Two simple NIDs, carrying six lines each, on the outside of a building
A German copper phone line termination box called Abschlusspunkt LinienTechnik (APL, "Demarcation point")

In telecommunications, a network interface device (NID; also known by several other names) is a device that serves as the demarcation point between the carrier's local loop and the customer's premises wiring. Outdoor telephone NIDs also provide the subscriber with access to the station wiring and serve as a convenient test point for verification of loop integrity and of the subscriber's inside wiring.