"The oldest and strongest emotion of mankind is fear, and the oldest and strongest kind of fear is fear of the unknown."
H. P. Lovecraft
Weird Fiction can be weird in several ways that have nothing to do with the actual content of the story. If you consult the Wikipedia entry, you'll get a definition of Weird Fiction that is okay, as far as it goes, but really M. R. James was mostly a writer of ghost stories more than Weird stuff, but that's a quibble.
If you consult H. P. Lovecraft's extensive essay on Supernatural Horror in Literature, either via the online version here, or here or here, or if you are ambitious and willing to fork over money for dead tree printing of this essay then go here. However you decide to access the essay, if you read what the old dead dude from back East had to say on such stuff, you'll come away with an even keener sense of despair, alienation and a growing sense of cosmic horror in the pit of your stomach as you realize nothing he wrote on teh subject, no matter how often cited, has anything to do with how stuff is handled in the marketplace today. And if you want to buy your books away from the computer, that's a big deal.
You could try to sort out what the folks at Weird Tales are up to in this regard, but the last couple of issues I sampled just didn't really suit me. I'm old fashioned in some respects. I am a big fan of Clark Ashton Smith and prefer weird stories to have some actual weirdness in them, not just weird-like subsitute and definitely not any of that weirdLite stuff.
When I was a kid, back when I was reading Blavatsky and suffering from recurring fevers and pneumonia every fall and winter, I made my first sale of an illustration to a small press magazine called Weirdbook. It was a wonderful publication produced by W. Paul Ganley. The weirdness in Weirdbook was palpable, a very real thing. I remember reading my first Brian Lumley story in Weirdbook. It was through Ganley & Weirdbook that Titus Crow first entered the American weird/horror/dark fantasy scene. Back then weird was used as a perjorative, it had an almost Fifties-esque connotation of non-conformity bordering on the perverse or nasty. To be called weird back then was a major put-down, an insult. But I never saw it as such. Not after getting published in Weirdbook. After that weird was just fine by me.
To me, weird fiction combines any and every element that the writer wants to, incorporates any technique, and can encompass any situation both conceivable and inconceivable--it is weird after all--and it is something that partakes of just about all other genres the way a painter like Jackson Pollock uses colors or Van Gogh used texture. It's an approach that turns expectations arund, inverts the known and goes places that sanitized and approved commercial stuff rarely goes for fear of losing its audience. It can be rude, vulgar, challenging and uncomfortable like an insane cat-lady riding the bus at midnight with all her cats in a tattered cardboard box leaking urine onto the seat next to her. It can be purple prose that evokes conundrums, enigmas and paradox all in one sentence with or without a plot. It is a way of taking the old forms of mythology, especially the once popular stuff too low-brow for academia to concern itself with it, and convert it from a sow's ear of rubbish to the gold of something special and deeply, philosophically potent.
At least that's what it could be, might be, or used to be, but I'm not sure any one definition will ever really do the job as it shifts and changes in response to people's impressions, reactions and so one. You can't always tell the same joke a second time and get very many laughs. You have to move on. Grow. Adapt. Subvert the expectations and so forth and so on.