These are the definitions of flags used at DMTD:


 flag_greenGreen - The track is open and cars are running at speed.
flag_yellow Stationary Yellow - Proceed with caution, no passing until after the incident. Be prepared to alter your line if necessary.
 flag_yellowWaving Yellow - Warns of an immediate hazard on the course, probably on the driving line. You may need to slow down significantly. This flag is often used when a spin occurs. No passing until after the incident.
flag_passing Blue with Yellow Diagonal Stripe - The passing flag. A faster car is behind you... check your mirrors.
 flag_whiteWhite - Indicates an emergency vehicle or slow moving car is on the track.
flag_red Red - This flags indicates an emergency situation. Check your mirrors and bring your car to a controlled and complete stop on the side of the track offline. We may need to get emergency vehicles on the track quickly. Stay on the track... your hot muffler may start a grass fire.

flag_red Black with Red Circle - The meat ball flag indicates there is a mechanical problem with your car... something hanging, a leak, etc. Drive your car to into the pit entrance as soon as possible or pull off the track near the next corner worker station (if there is a fire). Pull off track if you are leaking fluid, don't continue and leak around the track.

flag_black Black Flag - Drive your car into the pit entrance and be prepared to talk with an event official.
flag_checkered Checkered Flag - The session is over... you should exit from the track at the next pit entrance