Plain English Meaning
The route an aircraft actually flies through the sky — where it goes side-to-side, how high it is, and when it climbs or descends along the way.
Full Definition
The actual three-dimensional tracks an aircraft follows through the air, described by its lateral course over the ground, its vertical profile (climbs, level segments, and descents), and its position over time.
Context Anchor
Seen in instrument procedure and NextGen discussions about using more precise, repeatable routes for aircraft.
Derivation
A simple compound of 'flight' and 'path.' Worth noting because in 'path' includes the vertical , not just the line on a map — a has shape in three dimensions.