A very short definition of women’s fiction would be stories about women by women. I’m not saying that a man couldn’t write women’s fiction. It’s entirely possible; however, I would advise that he use a pen name that’s feminine.
Where romances are about, well, romance, women’s fiction is more about relationships. Where a romance most often ends with the main characters winding in a satisfying relationship of some sort, women’s fiction can end with a woman facing life without romantic entanglements. When I say relationships, I don’t necessarily mean those between a man and a woman. Women’s fiction, a good deal of it anyway, contains stories about siblings, mother-daughter relationships, friendships, and the relationships between mothers and their children.
Women's fiction is longer and uses that space to develop multiple point-of-view subplots that are deeper, more descriptive and more introspective than shorter novels.
There might be a guy waiting at the end of the heroine’s journey, but he never gets equal time or equal depth in his own journey. Whereas in romances the author gives her male character the same billing as her heroine, this is not the case in women’s fiction.
Commercial women’s fiction touches its reader at a more emotional level. As stated, the stories are about relationships, generational sagas and love stories, but more importantly the stories should touch on things that women readers can connect with in their own lives. Whether the reader cries or laughs out loud, women readers love reading that which tugs at their heartstrings.
New York Times Best-selling Author Nora Roberts says: "Women's fiction is a story that centers on a woman or on primarily women's issues, not necessarily the romantic relationship-based books I do, but the woman's story."
As usual, I like to remind readers that this definition is based on what the editors I work with want and on THEIR definitions of women’s fiction. Definitions of genres can vary WIDELY, so reading other blogs and resources about women’s fiction, if that is what you write, will give your background in your subject the breadth and depth needed to tackle this very complex genre. Good luck!