What Makes Something A Series?

I’ve been mulling series lately. What does it mean when we say something is a series?

The usual definition seems to be that the books share a main character or a set of characters who take turns being the main characters in the various installments. So, for example, all the Lee Child books about Jack Reacher are a series because they’re all about Jack (and a few other folks who come and stay for a bit), regardless of the fact that they’re set all over and each book has a different story line. Mysteries and thrillers seem to be the genres that follow this series format (think Kinsey Millhone, Thomas & Charlotte Pitt, etc.)

In romance, you typically get a “series” where the main characters (the couple that gets together at the end) switches from book to book, but generally they’re related in some way to the other couples who form up. So, when we look at my first three books, we have Kevin and Lydia in book one, Allison and Phil in book two (where Allison and Kevin were friends before and she helps out in book one), and then Karin and Jason in book three (Karin is Phil’s sister, and we meet her in book two.) So that makes a pretty clear romance “series”.

But here’s my conundrum…my next trilogy (Faith Departed, Hope Deferred, and Love Defined) have Kevin and Phil and Lydia and a few of the other folks from the first trilogy popping in. They all go to the same church. So can I consider the Remnants trilogy part of the larger Grant Us Grace series? (And if I consider them all part of the same series, does it need a larger name since I used Grant Us Grace as the trilogy name for my first three books?)

And we see Pastor Brown (who has cropped up in all but Kinsale Kisses at this point) helping out in A Splash of Substance as well.

So…since all the books are set in the same “world” – are they a series? Or are they simply multiple series in a shared setting? (And I guess the final, more important question is: does it matter to you as a reader?)