The document discusses the terms "idiosyncrasy" and "idiosyncratic". It defines an idiosyncrasy as an unusual feature of a person, and also as an odd habit. The term often expresses eccentricity or peculiarity. It notes that the term idiosyncrasy originates from Greek terms meaning "a peculiar temperament" or "habit of body". The document then provides an example of how jargon, or specialized language used within specific contexts, is considered an idiosyncratic rule of communication as it involves adjusting word choice based on relationships and contexts.