Definition
The distance from a present position to a fixed waypoint, measured along the programmed course, rather than in a straight line directly to the waypoint.
Plain English
How far you still have to travel to reach a waypoint if you follow your planned route, not the shortest line to it.
Context Anchor
Seen on navigation displays, moving maps, and flight-planning information when showing distance to a point along the planned route.
Derivation
The phrase combines 'along' (following the line of) and 'track' (the path actually being flown over the ground). So 'along-track' literally means 'measured along the path you are following.' This distinguishes it from a direct or straight-line distance.
Why Pilots Care
Supports accurate position awareness, timing, and fuel planning along a route.
Analogy
It is like measuring how far you have driven along a road, not how far your car is from the road if it drifts into a parking lot beside it.
Intuition Check
Do not read this as just any distance to a point. Along-track distance means distance measured along the planned route line.
Example Sentence 1
The GPS showed an along-track distance of 12 nautical miles to the next fix, even though the fix was only 9 miles away in a straight line.
Example Sentence 2
Monitoring along-track distance confirmed the aircraft's progress along the arrival route.