Plain English Meaning
The dashed white line painted down the middle of the runway. Pilots use it to keep the airplane straight and centered while taking off, landing, and rolling out.
Full Definition
The painted line of white dashes running down the middle of a runway, marking its lengthwise center and serving as the primary visual reference for aligning the airplane during takeoff, landing, and rollout.
Context Anchor
Seen during approach, landing, takeoff, and especially after landing while the airplane is slowing down on the runway.
Why Pilots Care
Tracking the centerline keeps the airplane equidistant from both runway edges, giving maximum margin if a blows, a hits, or momentarily . off the centerline reduces that and can to a .