Link popularity refers to the number of backlinks that point towards a website. The backlinks can be of two types: internal and external links. The links to a website from its pages are called internal links and the links from outside sources or other websites are called external links.
The high link popularity indicates that more people are connected to your site, and it has relevant information. Most of the search engines use link popularity in its algorithm while ranking websites in the SERPs. For example, if two websites have the same level of SEO, the site with higher link popularity will be higher than another site by the search engine.