What term refers to a partially punched impression in electrical boxes?

The term that refers to a partially punched impression in electrical boxes is "knockout." A knockout is a feature in electrical enclosures, providing an easy way to create an opening for electrical conduit or wiring. Knockouts allow electricians to remove a section of the box to accommodate incoming electrical cables, thus enabling a secure connection without compromising the integrity of the box itself. The design of knockouts facilitates installation and maintenance tasks, making electrical work more efficient.

Other terms like insulator, terminal box, and outlet hole are related to electrical components but do not specifically describe the partially punched openings found in electrical boxes. Insulators are materials that do not conduct electricity, terminal boxes are used to connect multiple wires, and outlet holes are openings for plugs but do not capture the function of a knockout.