Definition
A row of in-pavement red lights installed along a taxiway centerline as it approaches a runway, extending from the hold-short point toward the runway edge. The lights illuminate automatically when the runway is unsafe to enter — typically because an aircraft is on departure roll or on short final — warning pilots not to cross the hold line and enter the runway.
Plain English
Red lights set into the taxiway pavement that switch on to tell a pilot, 'Don't enter the runway right now — it isn't safe.' If the lights are on, stop and hold short.
Context Anchor
Seen while taxiing near a runway crossing or runway entry point at airports equipped with this lighting system.
Why Pilots Care
They give an immediate visual stop signal that helps prevent runway incursions and collisions.
Analogy
They work like a red traffic light at a road intersection: the light does not explain the whole traffic picture, but it clearly tells you not to go forward.
Intuition Check
Do not read “entrance” as permission to enter. In this term, the lights are placed at the runway entrance, and red REL mean stay out of the runway.
Example Sentence 1
As we taxied up to Runway 28R, the runway entrance lights came on, so we held short and called the tower to confirm our crossing clearance.
Example Sentence 2
After the departing aircraft cleared the runway, the RELs extinguished and I received clearance to taxi onto the runway.