HTML 5 (HyperText Markup Language Version 5) is the next major revision of the core language of the World Wide Web, HTML. HTML 5 specifies two variants of the same language, a “classic” HTML (text/html) variant known as HTML5 and an XHTML variant known asXHTML5.

The following is a cursory list of differences and some specific examples.

• New parsing rules oriented towards flexible parsing and compatibility
• New elements – section, article, footer, audio, video, progress, nav, meter, time, 
  aside, canvas, datagrid
• New types of form controls – dates and times, email, url, search
• New attributes – ping (on a and area), charset (on meta), async (on script)
• Global attributes (that can be applied for every element) – id, tabindex, hidden
• Deprecated elements dropped – center, font, strike, frames

• Learn HTML5
• What is HTML 5
• HTML 5 Tutorials

HTML 5 introduces new elements to HTML for the first time since the last millennium. New structural elements include aside, figure, and section. New inline elements include time, meter, and progress. New embedding elements include videoand audio. New interactive elements include details, datagrid, and command

Even well-formed HTML pages are harder to process than they should be because of the lack of structure. You have to figure out where the section breaks go by analyzing header levels. Sidebars, footers, headers, navigation menus, main content sections, and individual stories are marked up by the catch-all div element. HTML 5 adds new elements to specifically identify each of these common constructs:

• section: A part or chapter in a book, a section in a chapter, or essentially anything that has its own heading in HTML 4
• header: The page header shown on the page; not the same as the head element
• footer: The page footer where the fine print goes; the signature in an e-mail message
• nav: A collection of links to other pages
• article: An independent entry in a blog, magazine, compendium, and so forth