That is a distinct subset of direct navigation, useful by itself.
Some authors supply keywords.
These may well have been the reason for the page to have been found for the user by some search engine. When the author adds a reasonable number of pertinent keywords, they would be a useful fourth aid to search, and to characterize remote pages at more detail than the title of the page. As it is part of the head metainformation, it is not normally exposed to the user. We allude to the usefulness of stepping by links, referring to the anchors in the body, not the links to external URLs in the head. There may be other metainformation now hidden to the user in the head.