What do the different colored flags mean?

Motorsport flags are a standardized signaling system used across racing disciplines to communicate track conditions to drivers. Here's what the main ones mean: 

Green flag – Track is clear; racing/session has started or restarted. 

Yellow flag – Danger ahead (usually a crash or debris). Drivers must slow down and no overtaking is allowed. In some series, waved yellow means slow down more urgently than a stationary one. 

Double yellow flag – More serious hazard, often means be prepared to stop; slow down significantly. 

Red flag – Session or race stopped completely due to serious danger (bad crash, weather, track blockage). Cars must stop racing and return to the pits or a designated area. 

Blue flag – Shown to a slower driver to indicate that a faster one is approaching from behind. The slower car is expected to maintain a predictable line. Enforcement of blue flags varies from series to series: in Formula 1, a blue flag is a direct instruction to the slower car to let the faster one pass, and failing to do so after the third time a blue flag is shown can result in a penalty.  

White flag – The meaning varies by series. In F1 it can indicate a slow vehicle on track; in other forms of racing it traditionally means there is one lap remaining. 

Black flag – Driver must return to the pits immediately, often due to a penalty or car issue. Ignoring it too long can lead to disqualification. 

Black flag with an orange circle (meatball flag) – Mechanical issue on the car (like smoke or a loose part); driver must pit for inspection/repair. 

Black flag with a white cross – Unique to NASCAR, this is shown to a driver who has already ignored a standard black flag to indicate that their laps are no longer being counted until they pit to address the initial problem.  

Black and white diagonal flag – A warning for unsportsmanlike conduct; the next infraction could bring a black flag. 

Checkered flag – Signals the end of the race or session. 

Green checkered flag – Signals the end of a stage in NASCAR races. 

Yellow and red striped flag – Warns of a slippery track surface, often due to oil, water, or debris. 

Some series (like F1) also use light panels alongside or instead of physical flags, but they follow the same color-coded meanings