Plain English Meaning
A setting on a VOR/DME RNAV unit that lets the pilot fly a path running alongside the planned route, offset to the left or right by a chosen distance, instead of directly over it.
Full Definition
An RNAV operating mode in which the course deviation indicator (CDI) shows displacement from a course line that runs parallel to, but offset from, the original course between the active VOR/DME-defined waypoints. The aircraft flies a track parallel to the planned route at a pilot-selected lateral offset distance.
Context Anchor
Seen when using older VOR/DME RNAV equipment, especially when comparing raw VOR with guidance.