There are at least two topics here: what "literary fiction" might be in general usage, and what it means here at Chrons for this thread.
I'll skip the first, for now.
Here at Chrons, the term "Literary Fiction" was settled on for a catch-all place to discuss literary works other than those readily assignable to fantasy, horror, historical novels, or science fiction. Quite a few Chrons people evidently read nothing but books and stories in those categories, but quite a few Chrons people do read outside them.
Therefore, here at Chrons "Literary Fiction" includes what has often been called "serious literature," whether poetry or prose, but also travel books, memoirs, biographies, autobiographies, collections of letters, what used to be called middle-brow novels (cf. the discussion of mid-list authors), and so on. "Literary Fiction" would be sold (in the United States) in the Literature or Classics sections of bookstores, also in Poetry, and maybe even just Fiction categories. Here too would be the place to discuss books about books (other than genre ones). For example, if I wanted to talk about Colin Wilson's Poetry and Mysticism I'd start a thread here.
I myself can't stand to read nothing but fantasy, horror, or sf, one after the other, although when I was a youngster that's exactly what I did do. Now reading one after the other would tend to spoil the experience, I'm sure. The Chrons moderators have never scolded me for insufficient activity in the three categories most prominent here, for which I'm grateful.
I used the expression "serious literature" a moment ago. That's at best just a useful shorthand expression. It's awfully broad, since it would cover everything from the novels of Dickens to the works of 20th-century experimentalists -- and much more. Under this category we'd put Beowulf (right?) and Brideshead Revisited and Paradise Lost. I almost said the Anne of Green Gables books, but perhaps they would go under the Young Adult heading.
Does that help with the question of definition?