A Synod is a gathering of the faithful in order to listen to what the Holy Spirit is saying to the Church and asking her to be and to do. This gathering can involve the faithful in different ways: pastors with lay people, bishops with the other ordained ministries, pope with bishops, etc.
Pope Francis calls it “an exercise of mutual listening, conducted at all levels of the Church and involving the entire People of God” (Pope Francis, 18 Septemeber 2021). It involves encounter, listening and the discernment of spirits.
Synods taken many forms in church history and they are currently practised in the Church at all levels: from parish Pastoral Council meetings to Diocesan Synods, from Provincial Councils to Plenary Councils, from the assembles to the Synod of bishops to ecumenical Councils in which the bishops from across the world gather in Rome with the Pope. The practice of gathering to listen to the Spirit is as old as the Church herself, as shown by the "Council" of Jerusalem described in Acts of the Apostles 15. Synod-type mechanisms (listening, dialogue, discernment, deliberation) have always been used in monasteries and religious houses when making decisions. The conclaves, when cardinals meet to elect the new pope, is a synod event.
Pope Francis has sought from the beginning of his pontificate to invigorate and reconfigure the Synod of Bishops so that it might become more of an exercise of listening and discernment. Ever since his election in 2013, he has been teaching the Church about synodality and encouraging us to become a more synodal Church at every level. In an important speech on 17 October 2015, he said that the path of synodality is what God expects of the Church in the third millennium.
The word synod comes from the Greek synodos, which has the general meaning of "walking together". It offers an image of the Church as a pilgrim people, growing and developing on a journey of faith; a very different image from that of the Church as a static institution. A synodal Church expresses the Second Vatican Council vision of what sees the Church called to be: the People of God in which all baptized share the same dignity, and the essential distinction between lay people, clergy, bishops etc. is a difference of vocation and role, not of superiority.