The quick and inadequate definition of nonfiction
is that it is NOT fiction.
By the way, nonfiction is the correct spelling.
There is no English language word non, so it is incorrect
to write term as two words. In other words, there is no English
non fiction, only English nonfiction.
The prefix non means an absence. So when we say something
is nonfiction, we are saying there is no fiction in it. Fiction
is prose that is imagined, invented, fabricated, or feigned. So
nonfiction is prose that is not imagined, not invented, not fabricated
or otherwise cooked up by the writer.
Two types of writing
Prose, of course, is language that’s primarily concerned
about the ideas conveyed. It has little interest in how the ideas
sound.
Poetry, by contrast, cares about the music of the words
as much as the ideas.
I know this is boring, but you need to get these definitions down
cold. The fiction/nonfiction distinction is a basic literary concept,
roughly on the level of the 3-times tables.
If your students can't write a paragraph answer to the question
"What is nonfiction?" they shouldnt get a high school
diploma.
Imaginative writing genres
Let’s look at genres (types or classes) of the imaginative or fictive
side of writing so get a feel for what nonfiction isn’t. 
You can see that short stories and novels are fictional
genres. Most plays are prose fiction, but some (like
Shakespeare's plays) are in poetry form.
Novels, plays, and short stories employ setting, characterization,
and dialogue to relate a series of related events we call a story.
As you can see from the diagram, it is absurd to talk about a nonfiction
novel. A novel is fiction and there is no fiction in nonfiction.
That language is less apt to create confusion than saying "nonfiction
story." Of course, some students will misunderstand no matter what
you say. Be prepared to teach the fiction-nonfiction distinction
many times!
It is not totally wrong to use the term nonfiction story,
but it confuses students. They associate the word story with
fiction because the short story is a genre of fiction. The study
of English language and literature is full of such terminology traps
for the unwary student and his/her teacher.
To see what is nonfiction,
instead of what it is not, we’ll need a fresh page and another diagram.
created 05-May-2008; updated: 18-Sep-2008