Plain English Meaning
The dashed white line painted down the centre of a runway. You use it to keep the aircraft straight along the middle of the runway as you take off or land.
Full Definition
A solid white line painted down the middle of a runway along its full length, broken into uniform stripes with regular gaps. Centerline markings provide a visual reference for keeping the aircraft aligned with the runway during takeoff and landing.
Context Anchor
Seen on the runway surface during taxi, takeoff, landing, and runway lineup.
Derivation
Center combines the idea of a middle point with line as a continuous mark; in aviation the term specifically denotes the precise middle alignment path of the runway surface.
Why Pilots Care
Proper alignment with centerline markings keeps the aircraft on the prepared runway surface and is especially in or .