HTML5 is the next major revision of HTML. The last major revision, HTML4, has been a W3C Recommendation since 1997. The HTML5 draft was started in 2004. Development of HTML5 has fallen a bit behind and is still in the Working Draft stage. It should have been in the Candidate Recommendation stage by the end of 2010, but it is has now been pushed back to 2012. It is not even expected to reach W3C Recommendation until 2022 or later.
HTML5 will bring exciting new features such as a canvas for scripting drawings, images, and animation, audio and video support, and client-side database storage. Some Flash may be replaced by HTML5, as it could eliminate the need for third-party plugins such as Adobe Flash Player and Microsoft Silverlight for video-playback, and maybe even for some Flash games. Although HTML5 won't even read W3C Recommendation for over another decade from now, browsers are already beginning to support many of the HTML5 draft features. None are fully compliant yet, but hopefully we won't have to wait until 2022 to see a new web. One final note, not surprisingly, Microsoft Internet Explorer 9 is the farthest behind out of the top 5 Windows and Mac browsers.