- any danger or warning signal; specif., a red lamp, flare, etc.
- a red signal on a traffic light, indicating that a vehicle should come to a full stop
- The red-colored light that signals traffic to stop.
- Informal A command to stop.
(plural red lights)
- A warning light, especially as a traffic signal indicating "˜stop'.
- We ran three red lights on the way to the hospital.
- A sign of a brothel.
- (idiomatic) Denial to proceed. Ruling out of any possibility.