Posting these additional answers for you as they're too long for comments. I'm also digressing a bit from the original question by trying to offer a few insights into these different routes to publishing and why authors choose them. It is no longer a case of self-published books being the trash that traditional houses discarded:
No, vanity presses haven't disappeared, there are still plenty out there, many masquerading as traditional publishers and scamming authors out of money. Writer Beware offers insights into some of these scams but not every vanity press is a scam. However, no reputable agent or publisher will ever ask you for money. http://www.sfwa.org/other-resources/for-authors/writer-beware/
You could perhaps say that self-publishing (where none of the professional processes employed by a traditional publisher have been used) is the opposite to traditional publishing. But I feel that “opposite” is too strong because it suggests the processes are situated on the furthest sides from each other, when there is overlap. Particularly if a “self-published” book has been through the same processes (professional editing, typesetting, cover design, etc) as a traditionally published book. They are often indistinguishable from each other and these routes to publishing aren't distinct enough to be opposites.
Does everyone know the term ‘traditional publishing’? No. But, if you Google it, you'll find it’s a very prolific term, used by thousands of sources including “reputable” newspapers here in the UK like The Guardian and The Independent. But in my experience, very few people understand the publishing process at all unless they’re in the business. For example, when people ask about my writing and I say, ‘I’ve just finished the first draft of the next book’, they usually say, ‘Great! When’s it getting published?’ Fish-mouthed, I wonder how to even begin answering that question.
The one thing I do know is that self-publishing has a stigma that’s difficult to shake and unfair on indie authors who have gone through the same processes that a traditional publisher goes through. Which is perhaps why the term indie author was coined, to try to distinguish themselves from writers who had dumped an un-edited book on Amazon with a cover they had designed themselves on Photoshop.
The thing is that traditional publishing used to be the only route to market (unless you were rich enough to pay a small press) and here in the UK, when the NBA was still in place, publishers set the price of books and retailers had to adhere to those prices. It enabled publishers to subsidise the printing of less commercially viable but portentous books. When the NBA was abolished, the retailer was then able to set the price of books, and fat cats could afford to discount heavily. Independent book stores were no longer able to compete against the likes of big book sellers, supermarkets and Amazon and went out of business. You can read about the Net Book Agreement on Wiki - it’s very interesting.
Now, traditional publishers are being squeezed by retailers into selling their books at heavily-discounted rates. The fat cats refuse to stock at all if the publisher doesn't submit. Publishers push these massive discounts back on the author. So, if you buy a book for £5.99 from your local supermarket and the publisher sold it to them for £2.99, the author only gets 29p per copy. At that rate it’s almost impossible to earn back an advance and most authors never see any royalties. A friend of mine who’d won a prestigious literary award, sent me her royalty statement a few weeks ago and for six months of sales, her figures were in the negative. That’s because the returns of just a few hardbacks completely overshadowed respectable digital sales.
Because traditional publishers are being squeezed, they no longer have the marketing budget they once had. So, many traditionally published books hit the shops with little or no marketing and die a death on some dusty back shelf. If a traditionally published author wants to achieve success, they need to market the book themselves. However, they quickly realise that the services they are getting from a traditional publisher (editing, typesetting, cover design etc.) are being outsourced to independents they could have hired themselves. The one thing they really needed, the marketing efforts of a big publisher, isn’t done. Meanwhile, the publisher takes 90% of their profits and the agent takes 15% of their 10%.
So, authors, faced with signing contracts that bind them into selling their book (that perhaps took years to write) for a third of the price of a Batman Candy Stick, are looking for alternatives to traditional publishing. If they have to do their own marketing anyway, why not hire these independent editors, type-setters and cover designers and keep 70% of their profits through a print on demand service?
Many in-house editors who used to work in big publishing houses are now going independent and you can hire some very prestigious editors to work on your novel.
The Society of Authors, with Philip Pullman as president, is fighting for fairer traditional deals here in the UK, and this is a very interesting read: http://www.societyofauthors.org/News/Blogs/James-Mayhew/November-2016/James-Mayhew-Fair-Trade-for-Authors
As I said, I have digressed! I can only speak for the UK market, what is happening here in publishing, and why authors are choosing alternative routes to market instead of traditional publishing.