The document summarizes three HTML tags: 1) The <section> tag is used to create standalone sections within a webpage containing logically connected content. It divides the page into separate logical blocks and search engines usually search the section header for desired topics. 2) The <meta> tag defines metadata about an HTML document such as a character set, page description, and keywords. Metadata is not displayed but is machine parsable and important for search engines. 3) The <tt> tag specifies teletype text but is not supported in HTML5. It can be used within other tags like <p>, <pre>, and <code> to display text.