HTML Heading 4, represented as `<h4>`, is a tag used in HTML to define the fourth level of headings in a webpage. It is part of a hierarchy that includes six levels of headings, from `<h1>` to `<h6>`, with `<h1>` being the most important. Headings help structure content, making it easier for users and search engines to understand the organization of information. Using `<h4>` is beneficial for creating subheadings under a main heading, allowing for better content organization. Proper use of heading tags, including `HTML`, enhances accessibility and improves search engine optimization (SEO), as it helps search engines like `Google` index the content effectively.