Currently HTML5 is being developed by W3C (World Wide Web Consortium) as the next generation of web standard. The purpose of this release is to reduce the need for plug-in based rich internet applications (RIA) such as Adobe Flash, Microsoft Silverlight and Sun JavaFX. You can sneak a peek at the overview of HTML5 at the W3C official site here.
Until today the draft of HTML5 is still not finished yet. According to the W3C it will be released at late 2010. This next release of HTML5 will be supported by Microsoft, Apple and Google. Microsoft said they will support HTML5 in the next released Internet Explorer 9, you can test drive it here.
So what is the major improvement from HTML4 to HTML5? HTML5 will support video embedding in the HTML page without using any plugin. Nowadays many websites use video embedded into their pages. And the most well-known one is YouTube. To play video on YouTube you need the Adobe Flash plugin installed on your browser. But this has been an issue for mobile phones as it is still controversial in Apple iPhone and Apple iPad. Since nowadays mobile technology is widely used to access the internet, HTML5 is expected to provide much better content delivery to mobile technology.
Other than video embed support, HTML5 also introduces new APIs such as the canvas element for immediate mode 2D drawing, timed media playback, offline storage database, document editing, drag-and-drop, cross-document messaging, browser history management, and MIME type and protocol handler registration. HTML5 also improves error handling in parsing HTML tags.