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).
Plain English
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.
Context Anchor
Seen on the runway surface during taxi, takeoff, landing, and while confirming you are lined up with the correct runway.
Derivation
"Designation" comes from the Latin designare, meaning to mark out or point out. The runway designation literally points out which runway you are on by labeling it with its compass direction.
Why Pilots Care
These markings confirm runway orientation so the pilot can verify wind alignment and heading before takeoff or landing.
Intuition Check
Do not think of the number as an arbitrary runway name. In this context, the runway designation is based on the direction the runway points.
Example Sentence 1
Cleared for takeoff, the pilot taxied onto the runway and confirmed the runway designation marking 24 matched the clearance.
Example Sentence 2
Before takeoff the crew cross-checked the assigned heading against the runway designation marking on the pavement.