This applies to flights to select destinations from August 22, 2017, to December 13, 2017, and as with all flash sales and deals, it comes with a few caveats. All of the discounts apply to nonstop, one-way flights only, and blackout dates do apply. If you're unsure of anything, just use common sense and take a look at full terms and conditions before you book.
Hit up Southwest's website for the full list of flights on offer, both domestic and international, but you better do it fast, as these cheap flights won't stick around for long. The sale's only good until Thursday, July 27, and even before then, deals like this go pretty quickly, so get 'em while the getting's good.