Definition: Every so often, doctrinal matters would prompt officials of the Christian Church to call a meeting of some of their most senior officials. When bishops and other Church officials entitled to vote in Church councils were convoked from all over the world, such a council was regarded as an Ecumenical Council.
Ecumenical Councils considered matters of church-wide importance, such as holy days, the adoption of creeds, and specific heresies. Any decrees made by the council were, once confirmed by the pope, binding on all Christians.
If a large enough contingent of bishops refused or failed to attend the council, it was not properly considered ecumenical, and any resolutions passed by the body were not considered to have the authority of those of an Ecumenical Council.
The first Ecumenical Council was the Council of Nicaea, which was convoked by the Emperor Constantine in 325.
Examples:
The Council of Chalcedon was the fourth Ecumenical Council.
