That is how many Witchers have been sold by that witchiest of Witcher companies CD Projekt. That is more Witchers than anyone else has sold in the whole of human history - except probably not because the original book series is pretty popular. Also, it's not clear whether or not this includes countless free copies given away as parts of various deals, events, and things.
It is also the series' sixth birthday, which is kind of a weird (or entirely planned, given the way these sorts of announcements often go) coincidence. To celebrate both occasions, here is a graphic. A graphic with info. For example, did you know that Geralt was originally set to be played by comedian/actor/political revolutionary Russel Brand doing his best impersonation of Hugh Jackman's forearms? No? That's because I made it up. But there's real information on that image, in helpful numerical form, no less.
Eurogamer also has an interview and some other things. We do too, but our stuff is from before CDP sold six million Witchers and The World Was Never The Same Again. Because, I mean, whoa. That's a lot of Witchers. I don't even know which witch is which anymore, nor do I know how many witches a Witcher would bewitch if a Witcher could bewitch witches. These are uncertain times.
(Note: I may have taken a somewhat facetious tone throughout much of this, but I am legitimately pleased with this news. The Witcher series is excellent, and so far CD Projekt has run a tight, fan-focused ship. Applaud them, you scoundrels. Do it now!)