PlaysForSure is a certification given by Microsoft to portable devices and content services that have been tested against several compatibility and performance requirements. While it has become largely used among music stores other than iTunes, content providers aren't particularly thrilled about it since it is not compatible with the ubiquitous iPod.
Adding insult to injury, when Microsoft decided to enter the digital media player market with the Zune, the company itself did not embrace the PlaysForSure platform, instead going for an almost identical but still incompatible system to power its music player and store.
Now, Microsoft has added even more confusion to the DRM ecosystem by changing the PlaysForSure branding to "Certified for Windows Vista." The obvious problem here is that PlaysForSure works not only on Vista but on XP too. On top of that, plenty of things - including Microsoft's Zune - are "Certified for Windows Vista" but not necessary compatible with PlaysForSure. Talk about confusing the ordinary consumer.