Backlinks are incoming hyperlinks from one webpage to another website entirely. Any external website page that links to your site is considered and counted as a single backlink. Backlinks are strong indicators to search engines of a website’s value.
For example, if many high authority or trusted websites are linking to your site, that indicates to search engines your site too is also trust worthy. On the flip side, if many low value or high spam sites are linking to your website, that may indicate to search engines that your site cannot be trusted. An important part of a successful SEO strategy will include closely monitoring your backlinks and disavow with search engine tools as necessary.