black flag noun 4verb 1forms 3 noun4 •Any flag that has a black, or predominantly black, color. •A flag with a black color, used as a symbol of anarchism. •A racing flag with a black color, used in auto racing to summon a driver to the pits or to signal disqualification. •(informal, figurative) A cue, warning, or alert; a sign or signal that something is extremely wrong, often something criminal, hideous or atrocious; a extreme red flag. verb1 •To summon (a racing driver) to the pits by waving a black flag.Jack Sears was driving the famous John Willment Cobra roadster "39PH." Sears was black flagged, and after returning to the track, drove a race that is still talked about today. — 1994 formsblack flagged · black flagging · black flags