According to online ad network Chitika, 46% of all web users are already using HTML5-compatible browsers.
HTML5 is being developed as the next major revision of HTML (HyperText Markup Language). It is a core markup language of the World Wide Web. HTML5 is the proposed next standard for HTML 4.01, XHTML 1.0 and DOM Level 2 HTML. It aims to reduce the need for proprietary plug-in-based rich internet application (RIA) technologies such as Adobe Flash and Microsoft Silverlight.
Definition from: wikipedia