Slang is the relaxed street vocabulary never found in formal writing. Use slang, street slang, a slang word.
It marks a group as much as it names things: rhyming slang, prison slang, playground slang, and part of the point is that outsiders should not follow. It changes fast, which is why slang dates a speaker better than almost anything else. Note that slang is not the same as swearing, nor as dialect, which is regional and stable; and that yesterday's slang becomes today's ordinary word surprisingly often.
1nounslangThe relaxed street vocabulary never found in formal writing.
“Teenagers use so much slang that their parents often can't understand them.”
slang is informal vocabulary.
The word appears about 1756 meaning the vocabulary of tramps and thieves, and its origin is genuinely unknown. It is not related to language or lingo, despite the obvious guess.
First use appears c. 1756, meaning "special vocabulary of tramps or thieves", unknown. Not believed to be connected with language or lingo. Possibly derived from a gmq - source, then possibly related to Nordic language: Danish slænge, Icelandic and Norwegian Nynorsk slengja, Norwegian slenge, Swedish slänga (“to (carelessly) sling, throw, hurl; throw away, to dispose of; to flail”), with derivational nouns such as slæng, sleng, släng etc. Compare the compound: Danish slængenavn, Norwegian slengenavn, Norwegian Nynorsk slengenamn, Swedish slängnamn (“nickname, byname, informal name”) literally “sling-name”, and the phrases: Norwegian Nynorsk slengja kjeften, Swedish slänga käften (“to abuse verbally”) literally “to sling one's jowl”, Swedish slänga ur sig (“to say something hastily, carelessly, thoughtlessly”) literally “to throw out of oneself”, also Swedish slänga (“careless, nonchalant girl”) literally “sling + feminine suffix -a”.
Etymology from Wiktionary, CC BY-SA