Page Rank
Page rank is a mechanism used by the Google search engine to determine how important a webpage is.It is based on a number of factors, including the number of sites linking to that page.
Maths
The mathematics behind the Google page rank equation remains a closely guarded secret, as it is one of the key reasons for search engines success.
Patent
In 2006 Google applied for a number of patents to protect its page rank formula and application.