Plain English Meaning
A mode that lets the autopilot or flight director steer the airplane onto a chosen navigation course on its own, then follow that course once it gets there.
Full Definition
A flight director or autopilot mode that automatically captures and tracks a selected navigation course, such as a VOR radial or GPS course, by computing and flying the appropriate intercept angle from the aircraft's current position.
Context Anchor
Seen when using flight director or autopilot navigation mode, often after using heading guidance to aim the airplane toward the desired course.