A method of operating or a way of working, most commonly used in the phrase 'modus operandi' meaning someone's typical way of doing something.
From Latin operandi, the gerund of operari meaning 'to work.' Operandi is typically used in the phrase 'modus operandi' (mode of operating).
Police use the term 'modus operandi' to identify criminals because every criminal develops habits—a burglar might always enter through the back left window, and that pattern is unique enough to be identifying evidence!
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