HTML5 is the next foremost revision of the HTML standard overruling HTML 4.01, XHTML 1.0, and XHTML 1.1. HTML5 is a standard for presenting and structuring content on the World Wide Web.
HTML5 is basically the cooperation between the Web Hypertext Application Technology Working Group (WHATWG) and the World Wide Web Consortium (W3C).
The new standard includes features like video playback and drag-and-drop that have been previously dependent on third-party browser plug-ins like Adobe Flash, Microsoft Silverlight, and Google Gears.
The latest version of Apple, Mozilla Firefox, Safari, Google Chrome and Opera all supports many HTML5 features.
Also the mobile web browsers that come pre-installed on iPhones, iPads, and Android phones all have excellent support for HTML5.
HTML5 bring in number of new attributes and elements that helps in building a modern websites. Following are new and great features introduced in HTML5.
New Semantic Elements: These are like <section>, <header> and <footer>.
Forms 2.0: Advancement to HTML web forms where new attributes have been introduced for <input> tag.
WebSocket: It is a next-generation bidirectional communication technology for web applications.
Server-Sent Events: Server-Sent Events (SSE) events introduced by html 5 which flow from web server to the web browsers.
Audio & Video: We can insert in audio or video on our web pages without resorting to third-party plugins.
Geolocation: This feature make visitor able to choose to share their physical location with our web application.
Microdata: This feature lets us to create our own vocabularies beyond HTML5 and extend our web pages with custom semantics.
HTML5 is designed to be backward compatible with existing web browsers.If anyone is not familiar with any previous version of HTML, he should go through our HTML Tutorial before he explore further concepts of HTML5.
Write once and run it anywhere is the main feature of writing your mobile/table app using HTML5.
Build your application with open web standards to run on many platforms like Flash is a bad idea and yet Adobe started supporting HTML5 in mobile devices over flash.
Performance - Native application wins over HTML5 applications in performance basis. But you don't need native performance for all applications. So it is a disadvantage only in some cases.
Look and feel - In some cases native look and feel is better than HTML5 app.