Page Rank is trademark given by Google algorithm to any website. Google has an algorithm to count PR for specific website. PR=backlinks. So Google gives PR on the base of backlinks of a website.
http://en.wikipedia.org/wiki/Page_Rank has a good description of the algorithm. It's a google thing but I am sure other SEs have their equivalent of PR.
Actually no one can assess the algorithm of Google base on Page Rank. But based on my own experience you have to gather quality IBL to increase you PR.
So PR is calculated by a Google algorhythm... but is there any way to increase PR besides quality back links?
Actually, PR (PageRank) is google's meter to determine your link-popularity. The name PageRank is given from its co-founder Lerry Page. The tools desplaying PR do not desplay the excact figure of your pagerank but gives the approximate figures.
Yes, provide high-quality original content which your readers will find useful. Having good titles with appropriate keywords also helps
Pagerank is a measure of your sites authority. Some people say its worthless, but these are usually the same people who get slapped down a PR or two after an update
Well, I know sites with relatively low page rank that make loads of money (even from adverts) and other sites with high page rank which make no or little money. So, it is not the be-all and end-all.
Also there are many sites with high PR who are outranked by other sites with low PR... so, it does matter a lot but what is happening in fact? Does it have a direct influence on the outcome of ranking, or not?
Page rank is how Google see how important your site is. Usually webmaster are just trying to make money out of it.