Why Is It That Rome Claims to Be a “Church” but Says That Other Churches Are “Ecclesial Communities?”

Magisterial documents use the term church for the Catholic Church and for Christian denominations that maintain valid apostolic lines of succession (e.g., Eastern Orthodoxy). Those Christian denominations that have not maintained valid apostolic succession are called ecclesial communities. The purpose is to distinguish between groups that have maintained historic ties to the original apostles through apostolic succession and those that have not. It is not intended to be derogatory toward non-apostolic Christian denominations.