Main content
Area containing the main content of the page, where the background information and features are located (i.e. outside the menus, search or secondary areas of advertisements, related news...).
Usage
A main landmark (the role='main' is integrated into the <mic-main-content> component)identifies the primary content of the page.
When to use
Each page should have one main landmark. The main landmark should be a top-level landmark. When a page contains nested document and/or application roles (e.g. typically through the use of iframe and frame elements), each document or application role may have one main landmark. If a page includes more than one main landmark, each should have a unique label.
See the technical definition provided by WAI-ARIA: Main (role):
The main content of a document. This marks the content that is directly related to or expands upon the central topic of the document. The main role is a non-obtrusive alternative for "skip to main content" links, where the navigation option to go to the main content (or other landmarks) is provided by the user agent through a dialog or by assistive technologies. User agents SHOULD treat elements with the role of main as navigational landmarks. Within any document or application, the author SHOULD mark no more than one element with the main role.