HTML5 is the newest version of HTML.
HTML5 is the co-operation between World Wide Web Consortium (W3C) and the Web Hypertext Application Technology Working Group (WHATWG).
HTML5 works are still in progress. Most Major browsers started supporting the new features of html5 to some extent, may not be all but they are adding support for more tags over time.
HTML5 New Features
1) New Elements
2) New Attributes
3) Video & Audio
4) 2D/3D Graphics
5) Local Storage
6) Local SQL Database
7) Web Applications
HTML5 Key Rules
2) We should reduce the use of external plug-in (like flash etc.)
3) Better Error Handling
4) Extra markup to replace scripting
5) Development Process should be visible
HTML5 DOCTYPE Declaration
HTML5 Basic Page Structure