Disavow backlinks
PageRank is Google’s opinion of the importance of a page based on the incoming links from other sites. (PageRank is an important signal, but it’s one of more than 200 that we use to determine relevancy.) In general, a link from a site is regarded as a vote for the quality of your site.
Google works very hard to make sure that actions on third-party sites do not negatively affect a website. In some circumstances, incoming links can affect Google’s opinion of a page or site. For example, you or a search engine optimizer (SEO) you’ve hired may have built bad links to your site via paid links or other link schemes that violate our quality guidelines. First and foremost, we recommend that you remove as many spammy or low-quality links from the web as possible.
If you’ve done as much work as you can to remove spammy or low-quality links from the web, and are unable to make further progress on getting the links taken down, you can disavow the remaining links. In other words, you can ask Google not to take certain links into account when assessing your site.