(Abbr. KO) A portion of a metal enclosure which has been partially cut out but remains in place. It can be easily removed or "knocked out" to permit an electrician to attach switches, convenience outlets, conduit connectors, etc. Often referred to as a "KO".
A removable piece of an electrical box or panel that's "knocked out" to allow cable to enter the box.
something usually found on an outlet box, switch box, J-box, that needs to be knpcked out to accomodate wires