a. The total number of inbound links to a page of a web site
b. The subject matter of the site providing the inbound link to a page of a web site
c. The text used to describe the inbound link to a page of a web site
d. The number of outbound links on the page that contains the inbound link to a page of a web site

There are more factors but people should not be focussed to much at the pagerank when they are doing SEO. When you are doing SEO you want to end up high in the SERPs this also can be done with a low pagerank.

as mentioned by our one fellow.
PR is not the essential part for your site to be on top.
and if you are doing SEO and you want to end up high in the SERPs then this also can be done with a low pagerank.
hope you will get it....!

well in my point of view,
PageRank is a link analysis algorithm, named after Larry Page[1] and used by the Google Internet search engine..