Everyone seems to know everything about HTML5. But there is just so much information out there I thought I'd make a shorthand for everyone not already up to speed. HTML5 is a common term for the upgrade of all the basic web technologies. That tech that let's you build web sites (HTML, CSS and JS to be exact).
HTML5 can be used live today, but it won't become really wide spread until Internet Explorer 9 takes over the leading browser marketshare from IE 8. All modern browsers, including IE 9, handle almost everything that makes HTML5 so cool.
HTML5 was created to take the internet to the next level. Basically from Information sites to Functional Services more like apps. Basically people don't just want information these days but they want simple functions that give them access to the rightinformation. This is what apps do; give users the function and the bite sized chunk of information needed to use that function. In the same easy to use interface.
There is a huge difference between this paradigm and the earlier paradigm of the web. The change won't be very fast but it will come. The reason is that Mobile Web use is on the rise and the old paradigm of information heavy sites is simply really bad for that use. Already HTML5 is the norm for Mobile Devices, PCs are actually lagging behind.