I recently paid for a major airline ticket, and it got processed saying that the payment worked (on the website, and printed out the PDF). A moment later they canceled my order. Is this a bait and switch, or illegal false advertising for not confirming that it was available at that price (i.e. they changed the price after I clicked submit, and it said "confirmed")?
It is not a bait and switch, nor false advertising. It might be a violation of contract, depending on the exact wording of the TOS or other agreement with the site. Probably not.
"Bait and switch" refers to the tactic of advertising a specific product at a good price to draw one into a store (or to a site) and then claiming to be out of the advertised item, and attempting to sell the buyer a different item, usually one that is not as good a bargain. Even then, this is only illegal in most places if the seller did not have enough stock to meet reasonably anticipated demand. A notice such as "quantities limited" or "while supplies last" generally makes this legal. If no attempt is made to "switch" the customer to a different product, there is also usually no illegality.
Whether this is false advertising depends on exactly how it was advertised. If the TOS or ads contained wording such as "no purchase is final until confirmed with airline" then there is probably no false advertising, but the exact definition depends on the specifics of local law, and the details of the facts will matter a good bit.