A desktop operating system developed by Microsoft, released in 2013. Also known as Windows Blue. Please only use this tag if the question is specific to this version of Windows.
Released in October 2013, Windows 8.1 is a free upgrade to Windows 8 and is a desktop operating system developed by Microsoft. This particular version fixed most of the mistakes made with Windows 8 and replaced it very shortly after its release.
Note that many questions about this version also apply to Windows Vista, 7 and 8.