HTML5 is simply the latest version of the HTML specification. It is similar to HTML However HTML 5 contains much better support for media such as, an audio and video tag.
Apple has been promoting HTML5 as an alternative to Flash for video and other content on the iOS, citing performance reasons for not allowing the Flash runtime to be installed on iOS
Some examples as below:
In HTML, audio and video requires external software support.
In HTML5, audio and video has internal specifications and has separate tags ie <audio> and <video>.
In HTML, finding correct Geo-Location is impossible.
In HTML5, JS Geo-Location API helps in identifying location.
For information: go to http://www.w3schools.com/html5/default.asp