Microsoft just announced the names for its suite of Windows 8 products. In an attempt to simplify things, the company opted for just three major versions: the consumer-ready Windows 8, the more advanced and versatile Windows 8 Pro, and the tablet-friendly Windows RT.
Wait a sec, Windows what?
"RT" stands for runtime, according to Microsoft's blog post explaining the naming scheme. Windows RT is the version of Windows that will run on devices powered by ARM-based chips — typically mobile devices like tablets (but not phones, since those run Windows Phone). It's what we were previously calling Windows on ARM.
Why "runtime?" Windows Runtime (usually abbreviated WinRT) is technically Microsoft's developer platform for Windows 8. The next version of Windows uses a brand-new interface, called Metro, that works with both touchscreens and mouse-and-keyboard setups. WinRT lets developers create apps only once, so they run on both regular PCs as well as ARM devices.
Why should you care about any of this? You shouldn't — it's all inside-baseball stuff of interest only to enthusiasts, engineers and developers. And that's exactly why Windows RT is such a terrible choice for the name. The label is perplexing, insidery and underwhelming.