The meta HTML element is used to define metadata about an HTML document, such as character set, description, keywords, and viewport settings. This metadata is crucial for search engines, browsers, and web services to interpret and display content.

The menu HTML element was intended to define a list of commands or options, such as context menus or toolbars. However, its use is largely obsolete, and it is not widely supported in modern browsers.

The mark HTML element is used to highlight text within a document, indicating relevance or importance, typically rendered with a yellow background by default.

The map HTML element is used to define an image map, a collection of clickable areas on an image, in conjunction with area elements. Each area can link to different destinations, allowing for interactive images.

The main HTML element is used to encapsulate the dominant content of a document, excluding headers, footers, and sidebars, to improve accessibility and SEO by clearly defining the primary content area.

The link HTML element is used to link external resources to a document, such as stylesheets or prefetch requests, playing a crucial role in defining the document's presentation and behavior.