HTML is a standardized version of hyper text markup language. The web standards project developed in 1999 around the same time HTML 4.0 was released, followed by XHTML 1.0 in 2000. These versions where a slow development in the movement towards richer web development, but could not support the same type of applications that Flash type projects produce. Here is where HTML 5 comes in. HTML 5 was developed out of a collaborative effort of gun-ho designers and developers to structure HTML web and mobile applications that are richer, while supporting video and applications.
Not all browsers support all the functionality that HTML 5 could offer. Keep in mind HTML 5 support and feature detection is constantly changing.
A glimpse at features:
The doctype for HTML 4:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
Notice the prominent versioning of it.4.01. But here’s the HTML5 doctype:
No version number! HTML5 is the end of the idea that we can just release a new version of HTML and wait decades for people to update. From now on, the expectation is that you’re up to date–you’re using the latest browsers with the latest standards and the latest technologies. If you’re not, we’ll still display your content, but the internet is done pandering to the lowest common denominator.