What is HTML5?

Just have same question like you in the first time learning HTML5 and I figure it out from sitepoint.com with very simple definition and easy to understand.

The easy answer is that it’s the latest version of HTML. But that doesn’t tell us much. Specifically, HTML5:

With HTML5, we can now embed audio and video natively within HTML documents. We can use inline SVG (Scalable Vector Graphics) markup.We can build more robust form experiences, complete with native error checking.We can create games, charts, and animations using the canvas element. Documents can communicate with each other using cross-document messaging. In other words, HTML5 is much more of an application platform, not just a markup language.

DOM-ination change in HTML5 world

interface turned each element of an HTML page into an object that could be created, moved, modified, or deleted using a scripting language. Now we could add animation or interactivity to our web pages, even if we had to wait ages for them to download over our super-slow, 14.4Kbps modems.

The DOM was such a brilliant addition to the web that other browsers quickly followed suit. But not every browser implemented the DOM in quite the same way. Netscape Navigator, for example, used document.layers objects to reference the entire collection of HTML nodes. Microsoft Internet Explorer went with document. all. And web developers everywhere spent years struggling to reconcile the two. Opera andWebKit, for what it’s worth, followed Internet Explorer’s lead. Both browsers adopted document.all.

Eventually “DOM0” went from being a standard-through-implementation to a standard-through-specification with the Document Object Model (DOM) Level 1 Specification7. Rather than document.layers and document.all, we could use document.getElementById and document.getElementsByTagName. Today, all browsers support the DOM.

HTML5 Applets and Plugins

In the midst of all of this—the growth of HTML, the rise of the DOM, and the shift to XHTML—applets and browser plugins joined the party. To their credit, applets and plugins added functionality missing from HTML. For example, RealPlayer and Apple’s QuickTime brought audio and video to the web. With Java applets, you could run a spreadsheet program in your browser. Macromedia (now Adobe) Flash and Shockwave let us add all of the above, plus animations.

Applets and plugins, however, suffered from three major problems:

1. Users who don’t have the plugin (or the applet environment) can’t see the content.

2. Applets and plugins expanded the surface for internet-based security breaches.

3. They were commercial products, and required developers to pay a license fee.

What’s more, plugins and applets sometimes caused their host environment—the browser—to slow or crash.

So what we had on the web was a scenario in which:

• Browsers didn’t parse HTML according to the same rules.
• New markup languages offered few clear advantages over HTML but added overhead to implement.
• Plugins and applets offered additional functionality, but created security and stability issues for browsers and licensing costs for developers.

These are the problems that HTML5 solves:

• It incorporates features and grammars introduced by XHTML and XForms.
• It almost eliminates the need for plugins and the stability and security issues they may introduce.