Slang is an informal and sometimes private vocabulary that expresses the solidarity of a group such as teenagers, rap musicians, or sports fans; it is subject to more rapid change than Standard English. For example, the slang teenagers use to express approval changes every few years; cool, groovy, neat, awesome, phat, and sick have replaced one another within the last three decades. Sometimes slang becomes so widespread that it is accepted as standard vocabulary. Jazz, for example, started out as slang but is now a standard term for a style of music.

Although slang has a certain vitality, it is a code that not everyone understands, and it is very informal. Therefore, it is inappropriate in most written work.

Regional expressions are common to a group in a geographic area. Let’s talk with the bark off (for Let’s speak frankly) is an expression in the southern United States, for example. Regional expressions have the same limitations as slang and are therefore inappropriate in most writing.