Magisterium is a Latin term (from magister "teacher") designating the official teaching office of the authorized living teaching authority of the catholic orthodox Christian church. According to the Catholic Church the only correct and valid understanding of the revealed Christian doctrine of salvation and the Bible can be obtained only by taking account of both Sacred Scripture and Apostolic Tradition as interpreted by the authentic catholic Christian Living Magisterium under the promised guidance of God the Holy Spirit. The teachings of the Magisterium are magisterial teachings, most often set forth in magisterial documents, such as the Documents of Vatican II, or the promulgated teachings of ecumenical councils.
The Protestant doctrine of sola scriptura rejects any need for Apostolic Tradition and a Living Magisterium for a reliable interpretation of the Bible. Differences in doctrinal interpretations based solely on the text of the Bible alone has resulted in a multitude of different Christian denominations.
More generally, and less often, the term magisterium is used by writers as a dignified or ironically sarcastic reference to the authoritative magisterium of any religious, philosophical, educational, scientific, even political, institution or organization. It embodies and represents official teaching.
The Magisterium of the Catholic Church (catholicessentials.net) Defines differences between Solemn/Extraordinary Magisterium and Ordinary Magisterium, with scriptural references.