Merriam-Webster calls them "deliberate gross distortion(s) of the truth used especially as a propaganda tactic."
Wikipedia says they're "covert operations designed to deceive the public in such a way that the operations appear as though they are being carried out by other entities."
Official reports hype Big Lies. MSM scoundrels regurgitate them. Truth is systematically buried. Deception substitutes for reality.
False flags are pretexts for militarism, wars, occupations, colonization, resource theft, and exploiting populations for profit.