Definition
Fixed green lights installed across the approach end of a runway, marking the beginning of the landing surface available for use. They are part of the runway lighting system and are visible to pilots on final approach.
Plain English
A row of green lights showing where the runway begins. When you see the green line on landing, that is where you can start touching down.
Context Anchor
Seen during approach and landing, especially at night, when identifying the correct runway and the start of the landing area.
Derivation
Threshold comes from the Old English word for the strip of wood or stone at the bottom of a doorway — the line you cross to enter. The runway threshold is the line you cross to enter the landing surface.
Why Pilots Care
They confirm the exact start of the landing surface, helping pilots avoid landing short or confusing the threshold with other markings.
Intuition Check
Threshold does not mean a personal limit here. It means the marked beginning of the runway area that is available for landing.
Example Sentence 1
On short final the threshold lights came into view, giving him a clear picture of where the runway began.
Example Sentence 2
Threshold lights helped confirm the correct touchdown point before landing.