noun
1.
a. : a warning signal
four times the red light on the instrument board blinked — Time
especially : a red traffic signal
at a red light a snarl of traffic waited — Thomas Savage
b. : a cautionary sign : deterrent
the bill is a red light to labor, warning of what may lie ahead — New Republic
2. : a game in which players run toward a goal while the player who is it with his back to them counts ten and whips around on the phrase “red light” when any player he catches in motion must return to the starting line