Internet Explorer 9 is Microsoft's web browser released in 2011 that introduced several user interface enhancements and improved support for web standards like HTML5 and CSS3. It features pinned sites that allow websites to be launched from the Windows taskbar like applications. IE9 also includes a faster JavaScript engine, enhanced tab functionality, and hardware acceleration for graphics, video, and font rendering. However, it dropped support for Windows XP and removed some legacy features from prior versions.