Back course

The reciprocal of the localizer course for an ILS (Instrument Landing System). When flying a back-course approach, the aircraft approaches the instrument runway from the end on which the localizer antennas are installed.

Aviation Maintenance Technician Handbook — Airframe, p. G-4

Also defined in 1 more source

The reciprocal of the localizer course for an ILS. When flying a back-course approach, an aircraft approaches the instrument runway from the end at which the localizer antennas are installed.

Pilot's Handbook of Aeronautical Knowledge, p. G-5