Which HTML element is used to define the main content of an HTML document?

The

element is the correct choice for defining the main content of an HTML document because it is specifically designed to encapsulate the most important content of a webpage that is unique to that particular document. According to HTML5 specifications, the

tag signifies the primary content of the document, excluding headers, footers, navigation menus, and sidebars.

This helps search engines and assistive technologies identify the main content structure of the page, enhancing accessibility and improving SEO (Search Engine Optimization). The

tag can only appear once in a document, ensuring clarity in its role as the principal content holder.

While the tag contains all the content of an HTML document, it encompasses more than just the main content—it includes everything displayed on the page: headers, footers, sections, and other elements. The element does not exist in standard HTML, and

is intended for grouping related content within the document but does not define the main content exclusively. Thus,

is the most appropriate choice for this specific purpose.