Technorati is an online index that gathers together blog entries and news articles on common topics using the folksonomy created by the authors. Technorati calculates the number of indexed websites that link to a particular blog within the past 180 days and uses that to assign an Authority number. A blog's Technorati Rank is then determined by how close it is to the top of the Authority pile.
By limiting the time period for generating the Authority number, blogs with fresh and interesting content are rewarded over stale blogs that might otherwise rely on their seniority to remain in the rankings.