Plain English Meaning
An approach where the controller watches you on radar and tells you when to start and stop turning, because your heading instrument has failed and you can't fly assigned headings.
Full Definition
A radar-directed approach used when the pilot's heading indicator (directional gyro) has failed. The controller observes the aircraft on radar and issues simple turn instructions — 'turn left' or 'turn right' — and 'stop turn' commands, rather than specific headings. The pilot makes standard-rate turns until on final approach, then half-standard-rate turns after that, complying immediately with each instruction.