Posts which (we theorize) are good to show to new users, to get them excited about rationality. Posts listed here should be high-quality classics, should be accessible without having previously read the Sequences or anything else on LessWrong, and should somehow convince a certain sort of reader that rationality is important, and they want to read more about it. A good motivational intro post might argue the value of rationality directly, or it might point out a reasoning flaw which people recognize strongly in themselves, or it might introduce a rationality concept which is particularly sticky.
This tag will be treated as a special case in recommendations, and is configured such that it isn't displayed on posts and doesn't appear in search results when adding tags from a post page (but you can still apply it from here). If you aren't sure whether a post meets the criteria, use the discussion page, or just add it (someone else can downvote the tag's relevance later).