Google’s algorithm ranks your website by scanning links from all sources which lead to your website. While doing a link building campaign you may have engaged in buying some links from third party websites, asking bloggers to link back to your website through blog comments, digital PR, etc. Not all of them would be high-quality links which do complete justice to your website’s reputation. Hence you can make such links as no-follow using rel=”nofollow” in the anchor tag of the hyperlink of your website’s HTML code.