An identifier for the runway. For physical runways, the convention is to label runways by their heading, dropping the last digit. E.g. for Liverpool, runway 9/27 is facing approximately magnetic heading 90 degrees in one direction, and 270 degrees in the opposite direction. If an airport has parallel runways, these would then be marked Left, Center and Right, e.g. 9L, 9C, 9R. For operational runways, the runway identifiers specifies one direction only: either 9 or 27 in the Liverpool example.