**Definition:**
HTML, or HyperText Markup Language, is the standard language used to create and design web pages. It structures content on the web using elements like headings, paragraphs, links, and images.

**Key ideas:**
- HTML uses tags to define elements, such as `<h1>` for headings and `<p>` for paragraphs.
- It allows for the creation of links using the `<a>` tag, which connects different web pages.
- HTML can include multimedia elements like images and videos with tags like `<img>` and `<video>`.
- It is the foundation of web development, working alongside CSS and JavaScript for styling and functionality.

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