HyperText Markup Language
This is a free, online textbook offered by Wikibooks. "HTML is a markup language used in most of the pages of the World Wide Web. HTML files are text files that, unlike completely plain text, contain additional formatting markup—sequences of characters telling web browsers what parts of text should be bold, where the headings are, or where tables, table rows and table cells start and end. HTML may be displayed by a visual web browser, a browser that reads the text of the page to the user, a Braille reader that converts pages to a braille format, email client, or a wireless device like a cellular phone."