The original meaning of cant was a secret language supposedly used by rogues and vagabonds in Elizabethan England. This Thieves' Cant was a feature of popular pamphlets and plays particularly between 1590 and 1615, but continued to feature in literature through the 18th century. There are questions about how genuinely the literature reflected vernacular use in the criminal underworld. A thief in 1839 claimed that the cant he had seen in print was nothing like the cant then used by gypsies, thieves and beggars. He also said that each of these used distinct vocabularies, which overlapped; the gypsies having a cant word for everything, and the beggars using a lower style than the thieves.
In modern times "Cant" is used sometimes to refer to Shelta (alternatively known as Sheldru, Gammon, or The Cant), the cryptolectic language of Irish Travellers based on Irish and English. Indeed the word cant is wrongly believed to be derived from the Irish word caint, "speech, talk". In Scotland, it refers to the mix of Romani, Scottish Gaelic and Scots used by Scottish Gypsies and Travellers. Scottish Highland Travellers also used a form of Gaelic backslang known as Beurla-reagaird.
An example of a cant language which has been introduced widely into the mainstream is the Polari language which was used extensively in the BBC radio series Round the Horne during the 1960s.
Another example of cant is used in the play Our Country's Good by Timberlake Wertenbaker. The convicts speak in Cant.
Nadsat in the book and movie A Clockwork Orange is, for all intents and purposes, a cant; in the book, Alex DeLarge also mentions that one of his cellmates in "Staja (State Jail) 15" tells long stories in "old-time criminal" slang---a short sample is given, which is clearly in some form of cant.