The term colloquial refers to a style of writing that conveys the effect of informal spoken language as distinct from formal or literary English. As a noun, the term is a colloquialism.
A colloquial style is commonly used, for example, in informal emails and text messages. You wouldn't use it where you need to sound professional, serious, or knowledgeable, such as in presentations, meetings, business letters and memos, and academic papers. As a literary device, it would be used in fiction and theater, especially in dialogue and internal narration of characters. It's more likely to be in lyrics as well.
Colloquial writing is a conversational style, but it's not writing exactly how you talk, either, Robert Saba said. "To do that would be bad writing - wordy, repetitive, disorganized. A conversational style is a default style, a drafting style, or point of departure that can serve as a consistent foundation for your writing. It is the style of a painter doing sketches for a painting, not the painting itself." Conversational writing as a style, then, is still more refined, composed, and precise than talking because of the ability to self-edit and polish the words.
On using the conversational style in essays, critic Joseph Epstein wrote,
"While there is no firmly set, single style for the essayist, styles varying with each particular essayist, the best general description of essayistic style was written in 1827 by William Hazlitt in his essay 'Familiar Style.' 'To write a genuine familiar or truly English style,' Hazlitt wrote, 'is to write as any one would speak in common conversation who had a thorough command and choice of words, or who could discourse with ease, force, and perspicuity, setting aside all pedantic and oratorical flourishes.' The style of the essayist is that of an extremely intelligent, highly commonsensical person talking, without stammer and with impressive coherence, to himself or herself and to anyone else who cares to eavesdrop. This self-reflexivity, this notion of talking to oneself, has always seemed to me to mark the essay off from the lecture. The lecturer is always teaching; so, too, frequently is the critic. If the essayist does so, it is usually only indirectly."
One should not go too informal in writing, either. According to Tracy Kidder and Richard Todd, "Breeziness has become for many the literary mode of first resort, a ready-to-wear means to seeming fresh and authentic. The style is catchy, and catching, like any other fashion. Writers should be cautious with this or any other stylized jauntiness - especially young writers, to whom the tone tends to come easily. The colloquial writer seeks intimacy, but the discerning reader, resisting that friendly hand on the shoulder, that winning grin, is apt to back away."
Mark Twain's Style
In fiction, Mark Twain's skill with dialogue and ability to capture and portray dialect in his works are highly lauded and make his style and voice distinct. Lionel Trilling described it: "Out of his knowledge of the actual speech of America Mark Twain forged a classic prose… Twain is the master of the style that escapes the fixity of the printed page, that sounds in our ears with the immediacy of the heard voice, the very voice of unpretentious truth."
See this example from "Adventures of Huckleberry Finn," 1884:
"We catched fish and talked, and we took a swim now and then to keep off sleepiness. It was kind of solemn, drifting down the big, still river, laying on our backs looking up at the stars, and we didn't ever feel like talking loud, and it warn't often that we laughed - only a little kind of a low chuckle. We had mighty good weather as a general thing, and nothing ever happened to us at all - that night, nor the next, nor the next."
George Orwell's Style
George Orwell's goal in writing was to be clear and direct and to reach as many people as possible, ordinary folks, so his was not a formal or stilted style. Richard H. Rovere explains it this way: "There is not much to do with George Orwell's novels except read them. Nor is there much to be said about his style. It was colloquial in diction and sinewy in construction; it aimed at clarity and unobtrusiveness and achieved both."
Orwell's opening line of the novel "1984" starts simply yet jarringly, "It was a bright cold day in April, and the clocks were striking thirteen." (1949)
- "Composing to Communicate." Cengage, 2017
- "Good Prose: The Art of Nonfiction." Random House, 2013
- "Introduction." "The Best American Essays 1993." Ticknor & Fields, 1993
- "The Liberal Imagination," Lionel Trilling, 1950
- "Introduction to 'The Orwell Reader,'" 1961