mark out the major regions of a page, such as main content, navigation, header and footer. Assistive technologies like screen readers use these landmarks for orientation: users can jump straight to the main content, identify navigation and move through the page in a structured way.
Important landmarks come from native elements:
<main>for the main region,<nav>for navigation areas,<header>and<footer>,<aside>for supplementary content.
Well-implemented landmarks are unambiguous and sensibly named, for example a navigation with an aria-label. Problems arise from duplicate or unnamed landmarks, several visible <main> elements, or regions rebuilt via a role attribute when a native element would suffice.