**Definition:**
HTML, or HyperText Markup Language, is the standard language used to create and design web pages. It structures content on the internet by using various elements and tags.

**Key ideas:**
- HTML uses tags to define elements like headings, paragraphs, links, and images.
- It forms the backbone of web content, allowing browsers to display text and multimedia.
- HTML documents are saved with a .html or .htm file extension.
- It is essential for web development, as it works alongside CSS and JavaScript.

**Why this topic matters in this category:**
Understanding HTML is crucial for anyone interested in web development and creating engaging online content.