The rel="nofollow" is a HTML attribute that tells search engines not to follow the link and not to credit it with any search engine optimization (SEO) benefits. This means that if a website links to another site using rel="nofollow", search engines will not count that link as a vote of confidence for the linked site. Nofollow links are often used for user-generated content like comments, forum posts, and social media profiles to prevent spam and maintain the integrity of search results.