Plain English Meaning

A setting on the GPS that locks it onto one waypoint and lets the pilot choose any course line running through it, instead of letting the GPS automatically move to the next point in the flight plan.

Full Definition

A mode of GPS navigation operation in which the receiver suspends automatic sequencing through a flight plan and instead provides course guidance to or from a single selected waypoint along a manually chosen course. The pilot selects the desired course (bearing) using the OBS knob or input, and the GPS displays course deviation relative to that bearing through the active waypoint, behaving like a traditional receiver tied to that waypoint.