Calling all DIY gurus

[Fish]

Does anyone know what the proper name for a bulkhead/plug that would allow you to put an electrical cord (like for a heater) through the side of an eheim cannister filter? I imagine it to be like those plugs in the top of powerheads where the cord goes into the body and prevents water from getting in.
Does that make any sense? Any ideas where I should start looking?
Top secret project .
TIA & Merry Christmas,

- Chad