First developed by Tim Berners-Lee in 1990, HTML is short for HyperText Markup Language. It is used to create electronic documents (called pages) that are displayed on the World Wide Web. Each page contains a series of connections to other pages called hyperlinks. Every web page you see on the Internet is written using one version of HTML code or another.
HTML code ensures the proper formatting of text and images so that your Internet browser may display them as they are intended to look. Without it, a browser would not know how to display text as elements or load images or other elements. HTML also provides a basic structure of the page, upon which Cascading Style Sheets are overlaid to change its appearance. One could think of HyperText Markup Language as the bones (structure) of a web page, and CSS as its skin (appearance).
Almost all the tags in this kind of code have an opening tag that contains the name with any attributes and a close tag that contains a forward slash and the name of the tag that is being closed. For tags that do not have a closing tag like the <img> tag, it is best practice to end the tag with a forward slash.
Each tag is contained within a less than and greater than angle brackets and everything between the opening and closing tag is displayed or affected by the tag.
This kind of files use either the .htm or .html file extension. Older versions of Windows (Windows 3.x) only allow three-letter file extensions, so they used .htm. However, both file extensions have the same meaning, and either may be used today. That being said, we recommend sticking to one naming convention as certain web servers may prefer one extension over the other.