HTML5 is the next major revision of the HTML standard superseding HTML 4.01, XHTML 1.0, and XHTML 1.1. HTML5 is a standard for structuring and presenting content on the World Wide Web.
HTML5 is a cooperation between the World Wide Web Consortium (W3C) and the Web Hypertext Application Technology Working Group (WHATWG).
The new standard incorporates features like video playback and drag-and-drop that have been previously dependent on third-party browser plug-ins such as Adobe Flash, Microsoft Silverlight, and Google Gears.
The latest versions of Apple Safari, Google Chrome, Mozilla Firefox, and Opera all support many HTML5 features and Internet Explorer 9.0 will also have support for some HTML5 functionality.
The mobile web browsers that come pre-installed on iPhones, iPads, and Android phones all have excellent support for HTML5.
HTML5 introduces a number of new elements and attributes that helps in building a modern websites. Following are great features introduced in HTML5.
New Semantic Elements: These are like <header>, <footer>, and <section>.
Forms 2.0: Improvements to HTML web forms where new attributes have been introduced for <input> tag.
Persistent Local Storage: To achieve without resorting to third-party plugins.
WebSocket : A a next-generation bidirectional communication technology for web applications.
Server-Sent Events: HTML5 introduces events which flow from web server to the web browsers and they are called Server-Sent Events (SSE).
Audio & Video: You can embed audio or video on your web pages without resorting to third-party plugins.
Geolocation: Now visitors can choose to share their physical location with your web application.
Microdata: This lets you create your own vocabularies beyond HTML5 and extend your web pages with custom semantics.
Drag and drop: Drag and drop the items from one location to another location on a the same webpage.
HTML5 is designed, as much as possible, to be backward compatible with existing web browsers. New features build on existing features and allow you to provide fallback content for older browsers.
If you are not familiar with any previous version of HTML, I would recommend to go through our HTML Tutorial before you explore further concepts of HTM5.