One answer to the question comes from the NoirCon website:
Noir tells the stories of tortured souls—losers, psychopaths, loners, obsessives—driven down deadly paths, following desperate plans that are doomed to failure.
If you’d prefer a dictionary definition, here’s one:
A genre of crime film or fiction characterized by cynicism, fatalism, and moral ambiguity.
In noir, like life, people want things. In noir, when people go after those things, all hell breaks loose. As Joe Clifford puts it: “I wanted this, I did that, and then it all turned to shit.”
Since ‘noir’ means ‘black’ in French, I think of noir as dark drama or melodrama. (‘Drama’ means ‘action’ in Greek.) The so-called ‘pulp’ and ‘hard-boiled’ stories of the 20s and 30s (e.g., Carroll John Daly, Erle Stanley Gardner, Dashiell Hammet) created the form and provided the foundation for contemporary noir. Much of noir uses genre conventions like the whodunit, police procedural, or detective story, but often pushes those boundaries with an existential or post-modern outlook. James M. Cain, author of the pioneering noir classics The Postman Always Rings Twice and Double Indemnity, claimed he wrote “love stories.”
Noir is very much in the eye of the beholder. To paraphrase Justice Stewart’s comment on pornography, you’ll know it when you see it. One of the nice things about the “noir” label is that it can apply to anything with an appropriately cynical outlook. Westerns can be noir, as can Science Fiction. Noir is more about attitude and feeling than anything else; history, biography, or even journalism could be described as noir. And what could be more noir than Moses leading the Hebrews out of Egypt and across the desert for forty years and yet, at the moment of his triumph, he gets to see the Promised Land but not actually enter it before he dies? Yahweh was one harsh SOB! (Thanks to Kenneth Wishnia for that thought.)
American author David Goodis wrote several novels in the noir canon. You can judge a book by its cover:
Jim Thompson, another post-WWII American writer, penned a number of noir novels:
Here in the States “noir” sounds more like “bar” and less like “bonsoir.” Remember that when you order a Pinot Noir!