It's a colloquial term for how much power / influence a particular webpage has over the backlink portfolio of URLs it links out to.
Link juice is the term used in the SEO world to refer to the value or equity passed from one page or site to another. This value is passed through hyperlinks. Search engines see links as votes by other websites that your page is valuable and worth promoting.
When you create a backlink on any site. Then link juice means that how much power or host site convert to your site is called link juice. I hope you understand that it link juice. For more details you can ask me any Question.
Link juice is slang used to describe and measure how much power a backlink passes onto another site and therefore strengthens it. If a website references another with a link (DoFollow), it transmits its positive properties to an extent (e.g. PageRank, TrustRank) and therefore gives a recommendation from the point of view of the search engine. The more link juice that flows from a linking to a linked site, the more emphatic this recommendation is.