Which of these is a secret language used by various groups to prevent outsiders from understanding them?

An argot is a secret language used by various groups 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, occupation, or hobby, in which sense it overlaps with jargon.

In his 1862 novel Les Misérables, Victor Hugo refers to that argot as both "the language of the dark" and "the language of misery."

The earliest known record of the term argot in this context 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 grammatical system. But such complete secret languages are rare because the speakers usually have some public language in common, on which the argot is largely based. Such argots are lexically divergent forms of a particular language, with a part of its vocabulary replaced by words unknown to the larger public; argot used in this sense is synonymous with cant. For example, argot in this sense is used for 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."