PageRank is a link analysis algorithm used by the Google Internet search engine 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. PageRank Uses in google toolbar: Measures popularity of a site ,Marketing value,Updated periodically, in google directory: PageRank: sort links within categories;Volunteers evaluate, classify, annotate;Open Directory project using PageRank.