An argot ( /ˈɑrɡoʊ/; French, Spanish, and Catalan for "slang") is a secret language used by various groups—including, but not limited to, thieves and other criminals—to prevent outsiders from understanding their conversations. The term argot is also used to refer to the informal specialized vocabulary from a particular field of study, hobby, job, sport, etc.
The author Victor Hugo was one of the first to research argot extensively. He describes it in his novel, Les Misérables, as the language of the dark; at one point, he says, "What is argot; properly speaking? Argot is the language of misery."
The earliest known record of argot was in a 1628 document. The word was probably derived from the contemporary name, les argotiers, given to a group of thieves at that time.
Under the strictest definition, an argot is a proper language, with its own grammar and style. But, such complete secret languages are rare, because the speakers usually have some public language in common, on which the argot is largely based. Argots are mainly versions of other languages with a part of its vocabulary replaced by words unknown to the larger public. For example, the term is used to describe systems such as verlan and louchébem, which retain French syntax and apply transformations only to individual words (and often only to a certain subset of words, such as nouns, or semantic content words). Such systems are examples of argots à clef, or "coded argots."
Specific words can go from argot into common speech or the other way. For example, "piaf" was a Parisian argot word for "sparrow"; after being taken up by the singer Edith Piaf, this meaning became well known in France and worldwide, and no longer serves the purpose of a secret language.