HTML 5 is the next major revision of the HTML language. Many major software players are working toward these enhancements to HTML since 2004.
While it is still under development, Google is using HTML 5 extensively to build their major communication & social networking product Google Wave.
HTML 5 will provide flexibility and interoperability to the developers, and enable more interactive and exciting websites and applications.
HTML 5 introduces and enhances a wide range of features including form controls, APIs, multimedia, structure, and semantics.