HTML5 is HTML. WOW! *Lights go off* I hope everyone right now is saying "ooooh I get it now" because I can't make it more clear then that. HTML5 is, by all means, the next version of HTML. After a split happened between native HTML and xHTML there had been a definitive divide in the way browsers would render each said type of HTML. This brought along with it a slew of doctypes and unnecessary conventions that were specific to one or the other. Now that xHTML has all but died many of it's features and it's ideas have come back into the native HTML strain. What's this mean? Far more semantic and near XML like tags in HTML5. As well as documentation / standardization for browser vendors to follow, when rendering said tags, and some sweet new attributes to some of our old favorite input elements.
So why is HTML5 important?
Well, if you have just become a web developer in the past 2-3 years you won't remember the dark times we had before then. Browser vendors made the rules and, to some extent, still do (many of them are involved in creating and documenting the W3C's specifications HTML5, CSS3 etc.). Long ago every vendor decided, on their own, how to render an HTML page. Making crucial decisions for the user when there was an error or ill-formatted code on the page. Unlike XML, browsers have always rendered HTML in some way even with errors in the code (XML refuses to render if there's an error). Many have said this is in bad taste but really there wouldn't have been an issue if there had been a standard way to treat errors and rendering way back when. Well, thank god for smart people! The big guys (Microsoft, Google, Mozilla Corporation etc.) are getting on the same page and making our lives simpler day by day. So be happy you live now and not in the days of uppercase, lowercase, "strict", "transitional", DTD's and all that madness.
HTML 5 features which are useful right now include:
Web Workers: Certain web applications use heavy scripts to perform functions. Web Workers use separate background threads for processing and it does not effect the performance of a web page.
Video: You can embed video without third-party proprietary plug-ins or codec. Video becomes as easy as embedding an image.
Canvas: This feature allows a web developer to render graphics on the fly. As with video, there is no need for a plug in.
Application caches: Web pages will start storing more and more information locally on the visitor's computer. It works like cookies, but where cookies are small, the new feature allows for much larger files. Google Gears is an excellent example of this in action.
Geolocation: Best known for use on mobile devices, geolocation is coming with HTML5.
The Web Hypertext Application Technology Working Group (WHATWG) began work on the new standard in 2004, when the World Wide Web Consortium (W3C) was focusing future developments on XHTML 2.0, and HTML 4.01 had not been updated since 2000. In 2009, the W3C allowed the XHTML 2.0 Working Group's charter to expire and decided not to renew it. W3C and WHATWG are currently working together on the development of HTML5.
Even though HTML5 has been well known among web developers for years, it became the topic of mainstream media in April 2010 after Apple Inc's then-CEO Steve Jobs issued a public letter titled "Thoughts on Flash" where he concludes that Adobe "Flash is no longer necessary to watch video or consume any kind of web content" and that "new open standards created in the mobile era, such as HTML5, will win" This sparked a debate in web development circles where some suggested that while HTML5 provides enhanced functionality, developers must consider the varying browser support of the different parts of the standard as well as other functionality differences between HTML5 and Flash. In early November 2011 Adobe announced that it will discontinue development of Flash for mobile devices and reorient its efforts in developing tools utilizing HTML 5.