Plain English Meaning
The line on the chart you fly along on your way toward a specific point. In holding, it's the leg that takes you back to the fix you're holding over.
Full Definition
The published or assigned course flown toward a fix, navaid, or holding point. In holding and instrument approach procedures, the inbound course is the specific track flown toward the holding fix or final approach fix, and it defines the orientation of the holding pattern or approach segment.
Context Anchor
Seen on instrument approach charts and in descriptions for holds, course reversals, and holding-in-lieu-of-procedure-turn entries.