HTML Heading 2, represented as `<h2>`, is a tag used in HTML to define the second level of headings in a web page. It is typically used to create subheadings under a main heading, which is marked by the `<h1>` tag. This helps organize content hierarchically, making it easier for both users and search engines to understand the structure of the information. Using `<h2>` tags improves the accessibility and readability of a webpage. Search engines like Google use these headings to index content effectively, which can enhance SEO (Search Engine Optimization). Proper use of heading tags contributes to a better user experience and can help improve a site's visibility in search results.