Informal language that feels current and often playful is slang. It consists of words and phrases that are regarded as very casual, sometimes ephemeral, and typically associated with particular groups—young people, subcultures, or professional circles. “Cool,” “ghosted,” and “lit” have all served as slang at different moments.

Slang marks in-group membership and can express attitudes of irreverence or solidarity. Because it changes rapidly, yesterday’s slang can sound dated today. Some slang terms eventually enter the standard lexicon; most fade. Dictionaries of slang attempt to capture the moving target, but the living language always outruns the printed record.

Writers who want to represent contemporary speech or a specific social milieu often incorporate slang. The risk is that the language will date the work or exclude readers who do not share the code. Used with a light touch and an ear for authenticity, slang can give dialogue and narration energy and specificity. Used carelessly, it can feel forced or opaque.