What is Back Course Switch in a aircraft?

It kind of does what it sounds like it does. It keeps the plane on a certain track or heading based keeping in line with what is behind you. The backcourse switch can also be used for approaches with runways that have ILS systems only on one end of the run way. If you are flying the approach to the opposite end of the runway that the ILS is servicing you may use the back course hold to capture the localizer and follow the course in to the runway for landing. The truck to this however is that on the ILS indicator in the cockpit everything shows in reverse. For example being off to the left would show up on the instruments as being off to the right and you would have to adjust accordingly.