Plain English Meaning
A painted line down the middle of a runway, taxiway, or road that a pilot uses as a straight line to fly along or taxi along.
Full Definition
A painted line running down the middle of a runway, taxiway, or road used as a visual reference to keep the airplane tracking straight along the surface or, when used as a ground feature during flight training, to provide a straight line over the ground for practicing straight-and-level flight.
Context Anchor
Seen when using outside visual references during basic flight training, and also on runways and taxiways while operating on the ground or near an airport.