A cut out operated by a wedge. The line terminals consist of a spring
bearing against a plate, the circuit being completed through their point
of contact. A plug or wedge composed of two metallic faces insulated
from each other is adapted to wedge the contact open. Terminals of a
loop circuit are connected to the faces of the wedge. Thus on sliding it
into place, the loop circuit is brought into series in the main circuit.

Synonym–Plug Cut Out–Spring Jack.