The Characteristics of an Informal Writing Style

Definition:

A broad term for speech or writing marked by a casual, familiar, and generally colloquial use of language.

An informal writing style is often more direct than a formal style and may rely more heavily on contractions, abbreviations, short sentences, and ellipses.

See Examples and Observations below. Also see:

Examples:

Examples and Observations:

"An informal writing style is a relaxed and colloquial way of writing standard English. It is the style found in most personal e-mail and in some business correspondence, nonfiction books of general interest, and mass-circulation magazines. There is less distance between the writer and the reader because the tone is more personal than in a formal writing style. Contractions and elliptical constructions are common. . . . An informal style approximates the cadence and structure of spoken English while conforming to the grammatical conventions of written English."
(G. J. Alred, C. T. Brusaw, and W. E. Oliu, Handbook of Technical Writing, 9th ed. St. Martin's Press, 2008)
"[T]he informal style, far from being merely a sloppy form of language, is governed by rules every bit as precise, logical, and rigorous as the rules governing formal language."
(A. Akmajian, et al, Linguistics: An Introduction to Language and Communication. MIT Press, 2001)

Informal Style in Electronic Communications
"As e-mail messages, text messages and social network postings become nearly ubiquitous in the lives of teenagers, the informality of electronic communications is seeping into their schoolwork, a new study says.

"Nearly two-thirds of 700 students surveyed said their e-communication style sometimes bled into school assignments, according to the study by the Pew Internet & American Life Project, in partnership with the College Board’s National Commission on Writing. About half said they sometimes omitted proper punctuation and capitalization in schoolwork. A quarter said they had used emoticons like smiley faces. About a third said they had used text shortcuts like 'LOL' for 'laugh out loud.'

"'I think this is not a worrying issue at all,' said Richard Sterling, emeritus executive director of the National Writing Project, which aims to improve the teaching of writing."
(Tamar Lewin, "Informal Style of Electronic Messages Is Showing Up in Schoolwork, Study Finds." The New York Times, Apr. 25, 2008)
Standard English and Informal Style
"[T]here is no necessary connection between Standard English and formal styles, or non-standard dialects and informal styles:
My mate is bloody knackered.
is informal style . . ., but it is also Standard English. On the other hand,
My friend be very tired.
which is stylistically less informal, is not in Standard English but some other dialect."
(Peter Trudgill, Dialects. Routledge, 1994)