What is Encyclical?
According to its etymology, an encyclical (from the Greek egkyklios, kyklos meaning a circle) is nothing more than a circular letter. In modern times, usage has confined the term almost exclusively to certain papal documents which differ in their technical form from the ordinary style of either Bulls or Briefs, and which in their superscription are explicitly addressed to the patriarchs, primates, archbishops, and bishops of the Universal Church in communion with the Apostolic See.