Dictionary.com Word FAQs
What is the difference between informal / nonformal, nonstandard, and slang words?
The status or stylistic labels informal and nonformal as well as colloquial are terms applied to written usage at the lowest level on the scale of formality. These are the most relaxed and the least constrained forms of written language, the language which we use when writing to close friends and relatives, and to colleagues and others whom we know well. These terms are perfectly acceptable Standard English as long as their use is limited to contexts appropriate for informality. In many dictionaries, the use of the label nonstandard is the most restrictive, applied to forms and usages that educated speakers and writers consider unacceptable. Slang is an extremely informal style of language that is vivid, often extravagant and facetious, in its striving for rhetorical effect.