Description is the fiction-writing mode for transmitting a mental image of the particulars of a story.  It’s through description that characters, plot, and setting are portrayed.  Description may also be used to help develop one or more of a story’s themes.  And, of course, how and when description is utilized throughout a story are important aspects of an author’s unique writing style. 

Description is one of the most widely recognized of the fiction-writing modes, together with dialogue, narration, exposition, and summarization.  Unfortunately (as with many concepts used in the craft of fiction) the term description has both broad definition and narrow definition, which may lead to confusion and ineffective use. 

As observed by Peter Selgin in By Cunning & Craft, “. . . all writing is descriptive.”  In fact, under the broadest of definitions, all of the other fiction-writing modes could be described as subcategories of description:
• What is action, if not a description of activity as it happens?
• What is narration, if not a descriptive account by the narrator?
• What is conversation (or dialogue), if not a description of speech?
• What is exposition, if not a descriptive transmittal of information?
• What is summarization, if not a descriptive summary of events?
• What is introspection, if not a description of a character’s thoughts?
• What is sensation, if not a description of a character’s perception of the senses?
• What is transition, if not a description of a shift in time, space, or viewpoint?
• What is emotion, if not a description of a character’s feelings?
• What is recollection, if not a description of recalled memory?
Such a broad definition has limited value in understanding fiction or writing it: it’s comparable to describing a poinsettia as a plant.  A more useful definition of description includes only those aspects of description not otherwise addressed through the other fiction-writing modes: description in its purest sense. 

Even a more narrow definition of description leaves quite a few issues to be addressed. 
• Which word is better than another?
• Not every detail may be included in the story, so which details of description should be selected?
• How much description is appropriate?
• How and when should concrete nouns be used instead of abstract nouns, or vice versa?
• How and when should active voice be used instead of passive voice, or vice versa?
• How and when should modifiers (adjectives and adverbs) be used to enhance description? 
• How and when should clichés be used or avoided?
• When should comparative description (similes and metaphors) be used?
• When should transmorphic description (anthropomorphism, personification, objectification) be used?
• When does description become too obtrusive?
• How may description be disguised?
• Should description be presented directly by the narrator of the story or should it seem to flow through a point-of-view character? 

Although description is one of the most widely recognized and appreciated fiction-writing modes, failure to appropriately define it (as it relates to other fiction-writing modes), diminishes the likelihood that description will be fully analyzed and understood by students of fiction.  Failure to identify and address the numerous issues faced by an author when presenting description reduces the likelihood that description will be utilized skillfully and to its full potential.

For more information about fiction-writing modes see
http://www.helium.com/items/197336-fiction-writing-modes-and-how-to-use-them