2.22 What is a Church Council?
A Church Council is a meeting at which the pope and the bishops, assisted by experts, examine questions to which the Bible has no ready-made answers. Often these questions arise in response to a heresy or false doctrine (denying or changing the truth about God).
The answers arrived at by the councils are part of the Tradition of the Church. Important councils are also called Ecumenical Councils, as they bring together representatives of the entire Church.
Regarding those observances which we keep and all the world keeps, and which do not derive from Scripture but from tradition, we are given to understand that they have been ordained or recommended to be kept by the Apostles themselves, or by plenary councils, whose authority is well founded in the Church. [St. Augustine, Letters, No. 54 (ML 33, 200)]