Plain English Meaning

The big painted number you see at the start of a runway. It tells you which way the runway points, based on a compass. If two or three runways run parallel to each other, a letter is added so pilots and controllers can tell them apart.

Full Definition

The large white number, and sometimes a letter, painted near the approach end of a runway that identifies it by its magnetic heading rounded to the nearest 10 degrees, with the trailing zero dropped. For example, a runway aligned to a magnetic heading of 273 degrees is designated 27. Where parallel runways exist, a letter is added to distinguish them: L (left), C (center), or R (right).

Context Anchor

Seen on the runway surface during taxi, takeoff, landing, and while confirming you are lined up with the correct runway.