The word ecumenical comes from a Greek word that means pertaining to the whole world. In Christianity it means pertaining to the whole Christian church, and describes the pursuit of unity in the Christian world, between Christian denominations, and the universality of the Church.
In the Catholic and Eastern Orthodox churches an ecumenical council is a council of nearly all bishops of the whole church, capable of infallible decisions on theological questions. Catholics construe "the whole church" as including only Catholics. Eastern Orthodoxy construes it as including only, and with the consent of all of, the Orthodox; which, they contend, since the Great Schism, consists of only the Eastern Orthodox .
See also Ecumenism.