The following definitions are all from HTML – Living Standard:
The body element: The body element represents the main content of the document.
The header element: The header element represents a group of introductory or navigational aids.
The h1, h2, h3, h4, h5, and h6 elements: These elements represent headings for their sections. These elements have a rank given by the number in their name. The h1 element is said to have the highest rank, the h6 element has the lowest rank, and two elements with the same name have equal rank.
The nav element: The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links.
The section element: The section element represents a generic section of a document or application. A section, in this context, is a thematic grouping of content, typically with a heading.
The article element: The article element represents a self-contained composition in a document, page, application, or site and that is, in principle, independently distributable or reusable, e.g. in syndication. This could be a forum post, a magazine or newspaper article, a blog entry, a user-submitted comment, an interactive widget or gadget, or any other independent item of content.
The aside element: The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography.It can be used for typographical effects like pull quotes or sidebars, for advertising, for groups of nav elements, and for other content that is considered separate from the main content of the page.
The footer element: The footer element represents a footer for its nearest ancestor sectioning content or sectioning root element. A footer typically contains information about its section such as who wrote it, links to related documents, copyright data, and the like.
The address element: The address element represents the contact information for its nearest article or body element ancestor. If that is the body element, then the contact information applies to the document as a whole.