Slang
Etymology
Of uncertain and much-debated origin, appearing in the eighteenth century first in reference to the special vocabulary of tramps and thieves. Various roots have been proposed, including Scandinavian dialect forms, but none is confirmed, so its own etymology is aptly murky.
noun · /slang/
Very informal vocabulary, often short-lived and tied to a particular group, used in casual speech rather than formal writing.
What it names
The playful, in-group, ever-renewing layer of a language — the words that mark you as current and as belonging.
Example
What counted as cutting-edge slang last year already sounds dated to teenagers now.
Related idea
Distinct from jargon, the technical vocabulary of a profession that aids precision; slang is about informality and social identity, not expertise. It shades into argot, the secretive in-group speech of a closed community, where slang is usually meant to be shared and enjoyed.