HTML5 was thrown around by the likes of Apple and Google. This is the next evolution of HTML, or Hyper Text Markup Language, which forms the backbone of almost every site on the Internet.
Assuming content providers sign on (and many are), this means you won't have to worry about installing yet another plugin just to listen to a song embedded in a blog or watch a video on YouTube. Similarly, this is a big deal for platforms that either don't support Flash (e.g., iPhone and iPad), or have well documented problems with it (e.g., Linux). It will be a particular boon to those smartphones for which supporting Flash has proven problematic.
ref:
HTML5 Triumphant: Silverlight, Flash Discontinuing - http://www.technologyreview.com/blog/mimssbits/27328/