Plain English Meaning
If you drew the runway's center stripe out into the sky beyond the end of the runway, that invisible line is the extended runway centerline. Pilots fly along it when lining up to land and when climbing out after takeoff.
Full Definition
An imaginary straight line projected outward from the centerline of a runway along its same heading, used as a reference path for aircraft on final approach and after takeoff.
Context Anchor
Seen in approach guidance, runway alignment, and visual approach slope indicator discussions.
Why Pilots Care
Maintaining alignment on this line keeps the aircraft centered on the runway, reducing the risk of landing off to the side or during final approach.