HTML is the payload that is transmitted through the processes of HTTP.
An HTML document includes text, formatting codes, references to other files, and links.
When you inspect the contents of a basic HTML document using a text processing application such as Windows Notepad or Unix's vi, you'll find that the document is actually an ordinary text file.
The file contains any text that will appear with the page, and it also includes a number of special HTML codes called tags.
Tags are instructions to the browser. They do not appear as written on the Web page, but they affect the way the data appears and the way the page behaves.
The HTML tags supply all the formatting, file references, and links associated with a Web page.