By Richard Nordquist http://grammar.about.com/od/il/g/Levels-Of-Usage.htm Definition:
A traditional term for register, or the varieties of language use determined by such factors as social occasion, purpose, and audience. Broad distinctions have commonly been drawn between formal and informal levels of usage.
Dictionaries sometimes provide usage labels to indicate the contexts in which certain words are generally used. Such labels include colloquial, slang, dialect, nonstandard, and archaic.
See also:
Diction
E.B. White's Diction and Metaphors in "Death of a Pig"
Nonstandard English and Standard English
Plain Style, Middle Style, and Grand Style
Style
Usage
Examples and Observations:
"Each of us employs a different level of usage (word choice) depending upon whether we are speaking or writing, upon who are our audience, upon the kind of occasion, etc. Different levels of usage are combinations of cultural levels and functional varieties. Included generally in such levels are dialect, ungrammatical speech, slang, illiteracies, and even colloquial language, as well as technical terms and scientific expressions."
(Harry Shaw, Punctuate It Right, 2nd ed. HarperCollins, 1993)
"Because the level of usage that is employed in various situations should be governed by the nature of each situation, any pronouncements concerning the acceptability or unacceptability of such expressions as 'It's me' would be presumptuous. However, in formal speaking and writing situations, in which you are often judged by the appropriateness of your speech habits, you should strive to take a formal approach to usage. In formal situations, if you should err, you should err on the side of formality."
(Gordon Loberger and Kate Shoup, Webster's New World English Grammar Handbook, 2nd ed. Wiley, 2009)
Mixed Levels of Usage
"It is possible to achieve unusual diction by mixing words from different usage levels so that learned literary terms rub