Aviation term (acronym: "no" + "RDO") used to refer to an aircraft without radio equipment. Under circumstances where such an aircraft is permitted to be flown, the pilot will indicate "NORDO" on the flight plan.
The term is also used to refer to aircraft with which radio contact has been lost. This can be particularly hazardous during IFR. FAA procedures for loss of radio contact are documented in FAR 91.185.