Definition
A row of steady, in-pavement red lights installed across a taxiway at a runway holding position, used during low-visibility operations to indicate that an aircraft or vehicle must stop and may not cross until the lights are extinguished by ATC.
Plain English
A line of red lights set into the taxiway surface that means stop. When ATC clears you to continue, they turn the lights off, and only then may you cross.
Context Anchor
Seen while taxiing at larger airports, especially during low-visibility operations under a Surface Movement Guidance Control System.
Derivation
“Stop” means to halt, and “bar” here means a line or barrier across a path. The term helps because the lights form a lighted barrier across the taxiway: they are not just marking the pavement; they are telling you to stop.
Why Pilots Care
They prevent runway incursions by enforcing a positive stop until ATC clears the aircraft to cross.
Intuition Check
Do not treat stop bar lights as ordinary taxiway lighting. If the red stop bar lights are on, they mean stop and do not cross.
Example Sentence 1
During the Category III taxi out, the crew held short until the controller extinguished the stop bar lights and cleared them to cross runway 27L.
Example Sentence 2
In low-visibility conditions the stop bar lights remained red until the tower confirmed the preceding aircraft had cleared the runway.