What is PageRank and how to improve sites to have better PR

“PageRank is a link analysis algorithm that assigns a numerical weighting to each element of a hyperlinked set of documents, such as the World Wide Web, with the purpose of “measuring” its relative importance within the set. The algorithm may be applied to any collection of entities with reciprocal quotations and references. The numerical weight that it assigns to any given element E is also called the PageRank of E and denoted by PR(E).” read more wikipedia.org

On Google site we can find that definition:
“PageRank relies on the uniquely democratic nature of the web by using its vast link structure as an indicator of an individual page’s value. In essence, Google interprets a link from page A to page B as a vote, by page A, for page B. But, Google looks at considerably more than the sheer volume of votes, or links a page receives; for example, it also analyzes the page that casts the vote. Votes cast by pages that are themselves “important” weigh more heavily and help to make other pages “important.” Using these and other factors, Google provides its views on pages’ relative importance.” Google Technology

Google PageRank sites is updated once per month. Information about PageRank is collected in Google Data Centers.

You can check Your PageRank here.
I have just added new tool to check all Google DataCenters for PR here.

There are same tips how to increase PageRank:
1. Add Your sites to Web Directories.
2. Exchange link with other webmasters.