HTML tag rel = “nofollow” attribute, which indicates to search engine that the link must not affect the “ranking (PageRank) of the Web site in the search index.
It is intended to reduce the number of false hits on search engines and improve the quality of the search. We often use it to link to other websites which we do not want to assign importance to search engines.
Example:
<a href="site-map.html" rel="nofollow">Sitemap</a>