Page rank algorithm is used to determine a webpage’s importance or relevance in the web dependant on certain criteria. The criteria may include numbers of word matches with the search terms, number of other webpages that link this one and/or cite it as a source, number of unique visits for certain amount of time etc. There are some techniques that try to fool the search engines like link farms, keyword spamming and a lot of meta tags. The last two are somewhat easier to be dealt with (simply by being ignored most of the time). Link farms are groups of sites that are producing links between each other pursuing higher link counts. The reason for such manipulations is the pursuit of higher page rank so even higher number of users will see the page which will lead to higher income. Link farms can be exploited by joining to them and get inbound linkage but refuse to add links for one’s own site to the sites from the link farm. Google’s toolbar tries to follow the intentional user model by counting the visits from actual users (i.e. not computer bots) to a website. Page ranks can be calculated either recursively or iteratively. One of the most important uses of page rank is its meaning to advertising.