How HTML differ from HTML5?

Answer 1

HTML5 is the version of HTML.The main difference between HTML and HTML 5 is that video and audio are not part of HTML while these both are integral parts of HTML5 specifications. 

Answer 2

HTML5 is an update to HTML4 only ;) Add and remove some tags.

Answer 3

To end up Remmae's answer I'm gonna say that you've some new tags available like:
<header></header>
<nav></nav>
<section></section>
<article></article>
<footer></footer>

Answer 4

HTML5 is an update of HTML4. This has been brought by an idea of mobile response first. Hence its easier to develop a hybrid mobile app in HTML5 than on old HTML versions.
Some of the differences include but not limited to additional functionalities, accelerated mobile development, media management, UI enhancements and integrations with other frameworks and programs.