What is Link Juice ?
Well that is an important part for the ranking of your Website in Google.
It is the amount of links that could point to your site, directly or through any another site.
It means that if a site links to your site, and that site is linked by another site with a lot of hits, then you begin to build up link juice to your site !
And for a same subject, link juice will make the difference in ranking between two sites !!!
So, the more back links you get the best you will rank on Google.