I've come across the phrase "upmarket contemporary women's fiction" several times when reading agent web sites. It's never explained. I'd hate to offend an agent by sending the wrong kind of query. What does upmarket mean? Does it mean happy ending or something else?
First, the answer to the question, then the rant.
First, upmarket is a way for agents to talk about where a book is going to sell best. Upmarket means they're thinking hardcover and trying to get some review attention. Downmarket means trade or paper original and they're just going to sell it till the cows come home. As for what the distinction is: that's a harder question. Upmarket is Chris Bohjalian, Elizabeth Berg, Alison Lurie.
Downmarket is Toni Sorenson Brown’s series Shirley You Can Do It (SMP); Patti Berg (Avon); and Robin Wells (Dorchester).
Now the rant: don't fine tune your queries like that. Query widely. So WHAT if some nitwit agent says "I don't understand why you sent me downmarket fiction when I clearly asked for upmarket". They can't reach through the computer and strangle you (Miss Snark has funded research for this but it's early days). Upmarket and downmarket are largely in the eye of the beholder and besides, writers mostly don't know diddly about this. That's the AGENT'S job to sort out.
Now, I'm not advising you to query agents with detective fiction if they only represent academic non fiction. But if an agent takes detective fiction, and you write that, query him/her. If an agent takes women's fiction, and you write that, query!
I've taken on projects (and sold them!) I'd have sworn I would not have. The writing just wooed me right out of my bunny slippers.
So, invest in stamps and a big old box of envelopes. Query widely. Don't worry about offending agents. The only way to truly offend us (rather than annoy) is to ignore us when you have a good project.