An anti-language is the language of a social group which develops as a means of preventing people from outside the group understanding it. It may use the same vocabulary and grammar, but in an unorthodox fashion.

Examples of anti-languages include cockney rhyming slang

Cockney rhyming slang

Rhyming slang is a form of phrase construction in the English language and is especially prevalent in dialectal British English from the East End of London; hence the alternative name, Cockney rhyming slang...

, CB slang

CB slang

CB slang is the distinctive anti-language, argot or cant which developed amongst users of citizens' band radio , especially truck drivers in the USA during the 1970s and early-1980s....

, the grypsera

Grypsera

Grypsera is a distinct non-standard dialect of the Polish language, used traditionally by recidivist prison inmates...

of Polish

Poland

Poland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...

 prisons and thieves' cant

Thieves' cant

Thieves' cant or Rogues' cant was a secret language which was formerly used by thieves, beggars and hustlers of various kinds in Great Britain and to a lesser extent in other English-speaking countries...

.

Analysis

The concept was studied by the linguist M. A. K. Halliday who used the term for the lingua franca

Lingua franca

A lingua franca is a language systematically used to make communication possible between people not sharing a mother tongue, in particular when it is a third language, distinct from both mother tongues.-Characteristics:"Lingua franca" is a functionally defined term, independent of the linguistic...

 of an anti-society which is set up within another society, as a conscious alternative to it, and which indicates linguistic accomplishments of the users in action. According to Halliday, "metaphorical modes of expression are the norm". He compiled a list of criteria for an anti-language.

1. An anti-society is a society which is set up within another society as a conscious alternative to it.
2. Like the early records of the languages of exotic cultures, the information usually comes to us in the form of word lists.
3. The simplest form taken by an anti-language is that of new words for old: it is a language relexicalised
4. The principal is that of same grammar, different vocabulary.
5. Effective communication depends on exchanging meanings which are inaccessible to the layperson.
6. The anti-language is not just an optional extra, it is the fundamental element in the existence of the “second life” phenomenon.
7. The most important vehicle of reality-maintenance is conversation. All who employ this same form of communication are reality-maintaining others.
8. The anti-language is a vehicle of resocialisation.
9. There is continuity between language and anti-language.