HTML stands for Hypertext Markup Language, and it's a code that defines the structure and content of a web page. HTML is a fundamental building block of the web, and it's used to tell a web browser how to display content like text, images, and other multimedia. 

Here are some things to know about HTML:

Markup: HTML uses markup to annotate content for display in a web browser. Markup includes special elements, such as <head>, <title>, <body>, and <p>. 

Tags: HTML elements are set off from other text in a document by tags, which are the element name surrounded by < and >. 

Compatibility: HTML is generally adhered to by all major web browsers, including both desktop and mobile web browsers. 

Version: HTML5 is the latest version of the specification. 

Filename extension: The filename extension for HTML is .html or .htm. 

Other technologies: HTML is often used with other technologies, such as Cascading Style Sheets (CSS) and JavaScript. 

Ease of use: HTML has a simple, text-based structure that's easy for beginners to learn and understand.