Link juice is a search engine optimization term that refers to the qualitative value, or juice, of an external link pointing to your web page that is being considered as a backlink (see ‘Backlink’ explanation) to help boost your search engine rankings.
Just as one refers to a car having “juice” when it is powerful, an inbound link has juice when it has such qualities as a high Google PageRank™ (see PageRank™ for further explanation), many relevant and high traffic web pages, and a strong opportunity to reach your target audience groups from an external website.