HTML, which stands for HyperText Mark-up Language is the ASCII coded instructions that web browsers follow to display a webpages.

You may view the HTML coded instruction of any webpage by clicking "View -> Source" on your web browser.

Related Articles:

What is DHTML?
Dynamic HTML

What is XML
eXtensible Markup Language

When you "View Source", you aren't actually "Viewing the Source"
Others can view and even steal your client-side scripts, but not your server-side scripts!