A heading in web content and document formatting is a title or subtitle used to introduce sections of content. In HTML, headings are marked up with


tags, with

being the highest level (usually the main page title) and

the lowest. Headings are crucial for structuring content, making it easier for readers to navigate and understand the hierarchy and relevance of the information. They also play a significant role in Search Engine Optimization (SEO) by helping search engines understand the content structure and key topics of a webpage, thus improving its visibility in search results. Good heading practices involve using keywords relevant to the content and maintaining a clear, hierarchical structure.