Windows 10's interface is defined, obviously, by the eponymous "windows." It's useful sometimes to have more than one layer of compartmentalization for tasks and ideas, though. For example, you might have a web browser and a PDF reader, each with many separate tabs. Along those lines, Microsoft just announced an upcoming (and completely optional) interface paradigm for Windows 10 called Sets.
Sets are, in Microsoft's own words, a way to "organize and resume multi-faceted tasks." The idea is that for any given task, Windows will create a "Set" for you that lives in a special desktop view. The Set is a group that puts all the apps you use for that task in a single tabbed window. When you need to take a break and come back to it, you can simply close the whole set, then bring it up later to resume where you were. Sets will initially be limited to Store apps, though.
Sets are intended to be used in combination with the Timeline feature also on its way in a future update. Timeline was supposed to debut with the Fall Creators Update, but it was delayed as Microsoft deemed it not ready for prime time. The feature creates a history of your actions on the computer so that you can revisit them later—like your browser history, but for apps and documents. Sets will integrate with your Timeline so that you can revisit earlier tasks more easily.
As a further development of its Continuum feature, Microsoft says that it plans to allow users to tie Sets to their Microsoft accounts such that they will be able to take their entire workspace with them from device to device. The company also says that Sets will eventually support even heavy-weight applications like Adobe Photoshop.
If all of this sounds like a disaster for your use-case (personally, it reminds me of Compaq TabWorks), don't worry. PC World says that Microsoft is adamant that all of the new features will be completely optional. Those looking forward to using a Sets-feature right now might be interested in Stardock's Groupy.
Windows Insiders riding the bleeding edge of updates should be getting a download pretty soon that will enable Sets and Timeline. The rest of us users will have to wait until sometime next year.