PageRankalgorithm is also known as link analysis algorithm.  It has been used by google. The algorithm may be applied to any collection of entities with reciprocal quotations and hyperlinked set of documents, such as the World Wide Web, with the purpose of "measuring references. The name "PageRank" is a trademark of Google, and the PageRank process has been patented (U.S. Patent 6,285,999 ). The numerical weight that it assigns to any given element E is also called the PageRank of E and denoted by PR(E).
The name "PageRank" is a trademark of Google, and the PageRank process has been patented (U.S. Patent 6,285,999 ). However, the patent is assigned to Stanford University and not to Google. Google has exclusive license rights on the patent from Stanford University. 
In other words, a PageRank results from a "ballot" among all the other pages on the World Wide Web about how important a page is. A hyperlink to a page counts as a vote of support. The PageRank of a page is defined recursively and depends on the number and PageRank metric of all pages that link to it ("incoming links"). 
Numerous academic papers concerning PageRank have been published since Page and Brin's original paper.[4] In practice, the PageRank concept has proven to be vulnerable to manipulation, and extensive research has been devoted to identifying falsely inflated PageRank and ways to ignore links from documents with falsely inflated PageRank
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