I THINK I HAD already earned an MFA in creative writing and published my first two novels before I ever even heard of a style sheet. Then, after I'd heard of it, I believe it was a few weeks more before I knew what one was.
So, to spare those in a similar boat, let me explain ...
Essentially, a style sheet is a brief document submitted with the first draft of a novel or any other lengthy manuscript. Its purpose is to keep your copyeditor from breaking out the hat pins and voodoo doll every time she hears your name.
In its simplest form, the style sheet is a list of proper names and unusual terms that are either unique to the work being edited (think Tolkien's Lord of the Rings trilogy) or so rarely used that the average person might never have heard of them.
So, when writing his books Placebo and Singularity, for instance, novelist Steven James might have turned in a style sheet indicating that his protagonist was, indeed, named "Jevin Banks," and that he was not simply repeating the same typo, over and over, every time he tried to type the name, "Kevin."
And, had I heard of style sheets when I wrote my second novel, Turn Four, I would have used one to let my publisher know that shooters refer to their expended cartridges as "brass" (as in, "They finished shooting and picked up their brass."). It would have saved me some correspondence with my copyeditor, who wrote to me, asking, "Brass what? You keep using the adjective without the noun that it's modifying!"
Thanks to style sheets, my editors and copyeditors all know that the past tense for making a scuba dive is "dived" (not "dove"), just as, in baseball, when a batter hits a fly ball that is caught for the out, he is said to have, "flied out." And they know that, when I arm a bad guy with an "AK-74," it is not a mistake; I am referring, not to the AK-47 Kalashnikov rifle made famous in a hundred low-budget action films, but to a later generation of automatic weapon created by the same Russian designer.
Creating a style sheet is easy, as long as I begin it at the same time that I start my novel. I keep a second file open, either in my laptop or on my AlphaSmart Neo, and every time I hit a proper name or an unusual term that I think might give an editor pause, I add it to the style sheet in alphabetical order, together with a note or definition.
For my major characters, I might include details such as hair color and eye color (yep, I've had 'em change mid-manuscript a time or two), what they do for a living, and other matters that we might need to keep straight for the life of the story. And when listing place names, I might include where they lie in relation to other places named in the book, so we don't wind up with a character driving west to get to a location that is south of him.
Creating a style sheet does more than make my copyeditor's life easier. Just the act of creating it makes me that much more conscious of the details of my book; it allows me to think of my story from yet another angle.
And when the email arrives at my publishers with not only the manuscript attached, but a style sheet as well, they know that they are in the hands of someone who is conscientious about the craft. It's a win for everyone, all the way around.
Plus I don't have to lie awake at night, worrying about that voodoo doll.