Windows 8.1 is an operating system developed by Microsoft as part of the Windows NT family of operating systems. It was released as an update to Windows 8 and was made available to the public on October 17, 2013. Windows 8.1 aimed to address some of the criticisms and feedback received from users and critics regarding the original Windows 8 release.

Key Features of Windows 8.1:

1. Start Button: One of the most notable changes in Windows 8.1 was the reintroduction of the Start button. While it didn't bring back the traditional Start menu from earlier versions of Windows, it did offer an easier way to access the Start screen.

2. Improved Start Screen: The Start screen in Windows 8.1 received various enhancements, including new tile sizes, background customization options, and improved search functionality.

3. Boot to Desktop: Windows 8.1 allowed users to boot directly to the desktop mode, bypassing the Start screen, which was a welcome change for many desktop users.

4. Snap View: Windows 8.1 introduced improved multitasking capabilities with Snap View, allowing users to resize and display multiple apps side by side on the screen.

5. SkyDrive Integration: Windows 8.1 integrated SkyDrive (now known as OneDrive) more deeply into the operating system, making it easier for users to save and access their files in the cloud.

6. Internet Explorer 11: Windows 8.1 came with Internet Explorer 11, which offered improved performance, security, and support for modern web standards.

7. Enhanced Search: The Search functionality in Windows 8.1 was enhanced to provide more comprehensive results, including local files, apps, settings, and web results.

8. Security Improvements: Windows 8.1 included various security enhancements, such as improved built-in antivirus capabilities with Windows Defender and support for biometric authentication with Windows Hello.