The sides of something, particularly the sides of an animal's body or a military formation; also means to position yourself at the side of something.
From Old French 'flanc' possibly from Germanic 'hlanca' meaning 'hip' or 'loin.' Used militarily since medieval times to describe attacking from the side.
A flank attack in military strategy is devastatingly effective because soldiers naturally watch forward—hitting them from the side they're not prepared for, which is why it's used in chess, business strategy, and actual warfare!
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