I've been reading your emails consistently since I subscribed to them. I was hoping to find the answer to my question "what constitutes a book series?" I've been a Technical Writer/Editor for more than 20 years in the computer field and a story teller/artist since I first held a pencil in the one-room school I attended for one year in Kentucky. While at Ohio University I fell in love with Love Stories and have been writing them since. Even after joining RWA and attending national and local chapter conferences and classes the definition of a series still eludes me. I might have a series confused with an anthology.
You're not alone in your confusion. Publishing has a lot of strange terms, and to add to the confusion, uses familiar terms in unfamiliar ways.
A book series is generally understood to be more than two books with the same main character/s, set in approximately the same venue, with a chronology.
An example of this is my client Gary Corby's Athenian mystery series.
The first book (The Pericles Commission) introduces us to the main characters: Nicolaos; Pericles (a historical figure as well as a character here); Nico's annoying younger brother Socrates; Nico's family; and, Diotima, a priestess who captures Nico's heart.
The book is set in Ancient Athens.
The second book (The Ionia Sanction) expands the world by sending Our Hero to Ionia, but it's still set in the same time period.
The rest of the books follow that pattern.
Readers love these books as much for the characters as the plots. I'm always a bit melancholy when I finish reading one of them because I love to hang out with Nico and the gang.
You might think of the Jack Reacher books as a series, but they are really connected stand alones, because each one has the same main character (and a few recurring characters over the now many books.)
Each book can be read independently of the others. There is no real narrative arc over the entire set of books.
This isn't a bad thing. I love the Reacher books with a passion. I'm melancholy when I finish reading one because I love hanging out with Jack Reacher (and because I LOVE how Lee Child writes.)
Kristan Higgins on the other hand writes true stand alones, which always breaks my heart because I love every one of her books, and want to spend more time with every character she's created.
The books are independent of each other, have no recurring characters, and there is no narrative arc for all of them.
When you're querying a novel, it should be something I can read as a stand alone. That is, it does not depend on reading something else to understand it, and the story and plot should feel complete in this book.
Most editors want to buy series, rather than stand alones. Thus writers must query a stand alone then quickly figure out how to turn it into a series of some kind. What KIND of series is up in the air. That's something to be discussed with your agent.
Yes, we decided to do that in order to torment you. One of the many perks of the job.