Backlink
Also called: external link or inbound link
A backlink is a link from one website to another. The number of backlinks to a website, as well as their quality and relevance, have a large share in that site's search engine ranking. The more external links, the better found. Here, directly related links and links from sites that themselves have many links count most heavily.
Increasing the number of backlinks for better findability is called link building.