From the book by Leo Donald Davis:
According to the Roman Catholic Code of Canon Law, an ecumenical council is an assembly of bishops and other specified persons, convoked and presided over by the pope, for the purpose of formulating decisions concerning the Christian faith and discipline, which decisions require papal confirmation. The persons entitled to participate in an ecumenical council are the cardinals, patriarchs, archbishops and bishops, the abbot primate and abbots general of the monastic congregations, the superiors general of the exempt orders and abbots and prelates of special jurisdictions. However, it is abundantly clear from the history of the first seven ecumenical councils that this neat definition has not always applied. Rather, the first seven ecumenical councils were all called by the emperor, the vote of the papal legates not subsequent approval signified papal adherence to conciliar decrees, all five patriarchs had to be present in order that a council be truly ecumenical and councils were sometimes only designated ecumenical by the action of subsequent ecumenical councils. Today Roman Catholics accept twenty ecumenical councils; the Orthodox and some Protestants only seven.