A Visual Guide to NASCAR Flags
Green Flag The green flag signals the beginning or resumption of competition.
During qualifying it indicates to the driver his qualifying laps have begun.
It is also displayed at the beginning of pit road to indicate the pits are open.
White Flag A white flag is displayed when there is only one more lap to go until the race conclusion.
If a caution comes out after the white flag is displayed, the race is concluded.
Checker Flag During a race the checker flag means the race has been completed and each car will be scored when it passes the start-finish line. During qualifying it is used to show a driver his qualifying attempt is complete.
Yellow Flag A yellow flag indicates there is a hazard on the race track and all drivers must slow down and line up behind the pace car.  Typically this flag is waved when there has been an accident or when debris is spotted on the track.
Blue Flag with Orange Diagonal This flag is displayed to a car, or group of cars, to let them know that the leaders are coming up behind them and that should be courteous and move over to let the lead lap cars race. This is the only flag that is optional.

A solid blue flag is used to warn drivers of hard to see problems, such a car car spun out around a curve. Used on road courses only.
Red Flag The red flag indicates that all competition must immediately come to a halt. This includes the drivers on the race track, all pit crews servicing cars on pit road, and/or all pit crew members repairing cars in the garage.
Black Flag The black flag is officially called the consultation flag. It means that the driver who receives it must come down pit road to respond to a NASCAR concern.  A penalty is usually given to a driver that has been black flagged.
Black Cross Flag When a driver does not pit within five laps of receiving a black flag, they will be shown the black cross flag indicating they are no longer being scored by NASCAR.
Yellow Flag with Red Stripes The yellow and red flag indicates that there is debris on the track.
This flag is only used on road courses.
Red Flag With Yellow Cross The red flag with a yellow cross is shown at the entrance of pit road to indicate the pits are closed. When all the cars have lined up behind the pace car, pit road opens and the flag is withdrawn.
Red & Black Flags The flagman displays the red and black flags together to indicate to the drivers the
practice session or knock-out qualifying has ended.
Crossed Checkered Flags The flagman displays two crossed checker flags to indicate to the drivers the race has reached it's halfway point.
Green Checkered Flags The flagman displays the green checkered flag to indicate to the drivers the current stage has reached its conclusion.