PR means Votes (dofollow links from other pages) to a particular page and it's directly proportional to your inbound link. By the way friends Next page Rank update date is coming and I have Written an article on this topic, Check out Expected dates of Next Google PR Updates By the way no one can say it exactly, all these are assumptions and based previous PR updates.
Inbound links are nothing but backlinks/incoming links. Obviously these links are important for google to measure your site's page rank.