GREEN FLAG (GO)
Start of a your session on the track, or the restart after running under a yellow flag.

YELLOW FLAG (CAUTION)
When the Yellow Flag is displayed there will be no passing unless directed for a particular car or cars by the Officials. The yellow flag indicates danger, and overtaking under yellow flag is always prohibited.  The yellow flag may have two meanings: One waved = slow down. Double waved = slow down , prepare to stop if necessary.

YELLOW FLAG WITH RED STRIPE (UNSAFE)
This  flag indicates there is oil on the track or other unsafe conditions.

BLUE FLAG WITH DIAGONAL YELLOW STRIPE (PASS)
Move Over Flag - Faster cars attempting to pass you (it is expected that a car not competitive with the field will extend this courtesy while being lapped. Do not move over but hold his line.

RED FLAG (DANGER)
This flag means something major has happened. Stop your car in a safe area as soon as possible.

BLACK FLAG  (UNSAFE)
A black flag means unsafe conditions (flats, excessive smoking, loose car parts, etc). Cars will be warned with a black flag in case of minor incidents. Rough driving will result in immediate removal from the track for the remainder of that race.

BLACK FLAG WITH ORANGE BALL (YOU DID SOMETHING STUPID)
This flag, sometimes called the MEATBALL flag, means that the turn workers have  noticed a problem with your car. Proceed around to the pit exit, exit the track and talk to the Pre-grid controller at Start/Finish about your mechanical problem.

WHITE FLAG (LAST LAP)
This is sometimes refered to as the COURTESY flag.  When waived there is one lap to go before the Checkered Flag.