You undoubtedly have heard people using the term HTML5 in different contexts, which has probably caused at least some confusion. Like most so-called technical terms that find their way into the general population, and frequently fall from the lips of not-so-technical people, HTML5 finding it's way into the general population in fact means more than one thing. At the most basic level, HTML5 refers to the next version of the markup language created by Tim Berners-Lee, which now has a governing body guiding its progress. The other meaning of the term makes reference to other technologies that compliment the markup language, as well as the idea of an Open Web, which we'll talk more about later in the chapter.
Believe it or not, people have been trying to develop full-featured, complex applications intended to be executed in web browsers for a long time. For the most part, the greatest challenge has been the fact that the technologies required to accomplish this goal haven't been fully available until relatively recently. The reason why it was so difficult to create large web applications using earlier versions of HTML was that HTML was not originally designed for this. However, as the Web has evolved, so has HTML.
One of the goals of HTML5 is to accomplish exactly that—to enable developers to create powerful, non-trivial applications that run completely over the Internet. Another major goal of HTML5 is to be completely backwards compatible, so that web pages used for other purposes (namely the hyperlinking of research documents) can still function the same.
Just as Tim Berners-Lee added the hyperlink tag to SGML (among other tags), HTML5 is basically just that—more tags (or more functionality) to the previous version of the language. While that is a good, general overview of what HTML5 is, there is a bit more to the story. Beyond the new tags added to the HTML specification, the term HTML5 also refers to this next step in the evolution of the Web.
Some people have called this Web 2.0 and others have simply called it the future. When I refer to this next step in the history of HTML, I'll be referring to the upgrades done to HTML, CSS, and JavaScript, since these are the three major technologies behind this new Internet, where web applications (including online games) are the center of attention, as well as one of the focuses of this book.