A meeting of the priest and lay representatives within a parish community.
A meeting of the priests and lay representatives from a group of parish communities in a diocese.
A meeting of a bishop and representatives of clergy, religious and laity. Matters of diocesan church discipline and procedure are discussed. Under the revised Code of Canon Law, it is also called a Synod, specifically diocesan to distinguish it from the various Synods of bishops.
The present Code of Canon Law was called into revision in 1959 by Pope John XXIII when he announced he would call for a General Council (Vatican II). The revision actually started in 1965 when Vatican II ended and it was completed and promulgated by Pope John Paul II in 1983.
A meeting of an Archbishop with the bishops of his Province; also called a Synod. Actually all councils from this level upwards are Synods though they may not be referred to explicitly as such.
Plenary or National or Regional Council
A meeting of all the bishops of a nation or region (of more than one nation eg Catholic Bishop's Conference of Malaysia, Singapore and Brunei).
General or Ecumenical Council
A meeting of all the bishops of the world along with the Pope, or his representatives. Its decrees must have the Pope's approval.