Genre fiction is also known as popular, commercial or category fiction.
It is usually sold in the form of mass-market paperbacks, with only the big boys and girls (the Stephen Kings and Ruth Rendells of this world) being published in hardback first.
I am speaking generally here, but genre fiction places a greater emphasis on plot than literary fiction or mainstream fiction.
And it places less emphasis on characterization, the exploration of theme, and "fine" writing.
This isn't to say that commercial fiction can't contain three-dimensional characters, an undercurrent of meaning in the form of a theme, and high-quality prose - because it can and does.
But fans of genre novels are first and foremost after a good, entertaining read - and to achieve that the novel writer must always keep his or her readers in mind and put the story first.
Here are some of the principal fiction genres...
Visit any good-sized bookstore and you will find sections of shelving dedicated to some, if not all, of these genres of fiction.
(For a more detailed look at each of these categories, read my detailed guide to the Fiction Genres.)
Within each of the principal fictional genres are dozens of sub-genres (and sub-sub-genres) and these constantly evolve as readers' tastes change over the years. So within the crime genre, for example, you have (to name just three)...
What if the novel you have in mind spans several genres?
Then you must decide what the principal focus of your novel is.
So if you write a horror novel with a large dose of romance thrown in, you need to decide if the central thrust of your plot is the horror element or the romance.
If it is the horror element, fine. If it is the romance, you are actually writing not a horror novel but a romantic one - a "paranormal romance" or "gothic romance" perhaps.
The reason it is important to know your specific genre, is that all novels within a genre will share similar characteristics, or elements that fans of that category will expect your novel to contain - and your novel must also contain these elements if you want to keep the fans happy.
Horror fans, for example, will expect your novel to be about ghosts or zombies (or whatever), not about love. They will happily accept a romantic sub-plot. But they won't be happy if the romance takes center stage.
Incidentally, these characteristics which are common to all novels within a particular genre are known as its "conventions", and I talk about these in more detail in this article: Book Genres and Conventions.
All you need to understand for now is that, if you decide to write genre fiction, you are committing yourself to more or less following the conventions of your chosen category.
What if you want to write genre fiction - a detective novel, say - but don't want to follow the conventions of that genre?
Then you don't have to (it is your novel and you should never write what you don't want to write).
Writing your novel in this way is fine, but understand it won't be marketable as a generic detective novel (because you don't provide what fans of detective novels want).
You can always get away with bending the rules of your chosen genre (in fact, it is a good thing if you do, as it will make your novel distinctive).
But go too far and your novel will have to be marketed as a mainstream or literary novel.
This is bad in the sense that you are turning your back on the ready-made audience for detective novels, but good in the sense that your book will potentially appeal to a much wider general audience.
Just don't fall between the gaps.
If your novel is not enough of a conventional detective novel to appeal to fans of that genre, but too much like a conventional detective novel to attract a mainstream or literary audience, your novel may not find an audience at all.
Next Step: Keep reading for a definition of the next of the three main types of novels: Literary Fiction...