Green flag is one of the seven flags used in NASCAR racing. The green flag is the simplest flag. Whenever the green flag is waved, cars are free to travel at full speed.
At the beginning of the race, a honorary starter will usually wave the green flag and then the flagman will take over on lap two.
After a caution, the green flag is once again waved to show the field that the restart is happening. The only two laps that the green flag can not be waved is the last lap (white flag) and the finish (checkered flag).