Let's talk about a dirty word.
MIDLIST. Some published authors seem to be quite worried about being called "midlist". But kids, I've got news. Almost everyone is "midlist", unless you are super of-the-moment and hot, or famous and old. I think it's time for a vocab lesson.
Frontlist: Booksellers and publishers use the term "frontlist" to describe all the brand-new books this season, the books that are in the catalogue but have never been in the store before. These titles have no sales history yet, and everyone is very excited about them because they are NEW and SHINY and ANYTHING CAN HAPPEN! (Yes, if an old title is reissued in a brand-new format, it is frontlist again).
Once books stop being imaginary and/or brand-spanking-new, they are no longer frontlist and they will start getting returned if they aren't selling. For grownup books, this is about an eight week window. Kids and teen books have a bit more time, generally until the next season's books come in, so four to six months, or maybe even up to a year if there is room on the shelf.
Backlist: Booksellers and publishers use the term "backlist" to describe the books that have been out for a while, the paperbacks, the perennials. Books that are no longer frontlist become backlist or go out of print. Titles that have earned out, and that sell for years after they've come out, or for lifetimes, or even for millenia, stay backlist. Flashy NYT bestsellers or trends be damned, backlist is where the consistent money is. A deep backlist allows publishers to survive. You might hear an editor say something like "this will backlist well" -- they mean that this is a title that may not do amazing numbers, but that they expect it to stay in print and sell steadily for many years to come. This is a very good thing.
"Midlist": This isn't really a term that booksellers traditionally use in the same way as frontlist or backlist. It is instead most often a pejorative, probably first used by a smart-ass, meant to sound like those terms, but really it just means "not hot", "meh", "Johnny Average."
I think this is something authors ought to reclaim. Look, unless you are superfamous and dead (Hemingway, Poe, Faulkner) or superfamous and filthy rich (Patterson, King, Rowling) or people who read the New Yorker and wear ironic glasses talk about your ass (Gladwell, Foer, Franzen), or you are on the NYT bestseller list right now or soon (Steifvater, Clare, Hopkins, Marr) ... YOU ARE PROBABLY "MIDLIST". Yes, you! AND YOU!
And yes, that probably means your book. Get over it. It shouldn't be an insult. It means you are normal. You haven't hit the bigtime, nor are your books being read by generations of schoolchildren, nor do people in other countries, or even other counties, know your name... and that's OK. It's Normal. Normal. Normal is not bad.