PR Juice means Page Rank juice often referred to as link juice too.
Page rank juice or link juice is the strength of the links targeting a specific page and the external links. On that page and the link strength which is passed to external sites, this is called link juice or PR juice.

There are 2 types of ‘Page Rank’….

The one that, you can see in the Google Toolbar (TBPR). This tool is like green or gray bar which based on 1 to 10 scaling. Google updates the TBPR about every 3-4 months… Note: We have been known that when Google will update the TBPR before minimum 2 weeks from exact date.

There is also the ‘real’ Page Rank of page. This Page Rank is actually on ranking algorithm. It is updated constantly by Google crawls new and old links of your web page. It is called ‘real’ Page Rank which is based on some logarithmic scale.

Page Rank might be calculated as follows:

Real Page Rank ———————————————-TBPR
1-5——————————————————————-1
6-25——————————————————————2
26-125—————————————————————3
126-625————————————————————-4
626-3125————————————————————-5
etc. up to————————————————————10