A Metal Gear Solid V Definitive Edition has appeared on several online shops, including Amazon Japan and NetGames.de. While Amazon has already removed the listing, the latter still has it on their site. The release date is October 30th, though this may of course be just a placeholder.
If this is indeed a real thing, it will probably be a bundle of Ground Zeroes and The Phantom Pain, as well as the separately released costumes and DLC. For now we will have to wait for official confirmation by Konami.
Update 16/8: the Definitive edition (simply called Metal Gear Solid V Definitive) has also been listed on the Dell website (which also sells video games). The release date mentioned here is October 11, 2016, for $50. On the store listing, the PS4 version seems to be mixed up with the upcoming NES Classic Edition console, while the XB1 version lacks a description and image altogether. Still no official word from Konami.