Slang is vocabulary (words, phrases, and linguistic usages) of an informal register, common in spoken conversation but avoided in formal writing. It also sometimes refers to the language exclusive to the members of particular in-groups in order to establish group identity, exclude outsiders, or both.
Popularized in English during the mid-18th century, “slang” referred specifically to the lexicon of tramps and thieves. It is most likely Nordic in origin, derived from the old phrase slengja kjeften, which literally meant “to sling the jaw” (κρεμάω το σαγόνι) but which carried the implication “to abuse with words.”
