Fraternal delegates are official delegates, who attend major assemblies of a friendly body as a formal expression of the fraternal bonds.
In politics, that is customary among fraternal parties.
In religion, it happens between churches engaged in an ecumenical process. Thus the Holy See invited to Rome for the Roman Catholic Church's 14th Ordinary General Assembly of the Synod of Bishops in October 2015, on family, 'fraternal' delegates from Orthodox churches (the Greek-Orthox Ecumenical Patriarchate of Constantinople, Russian-Orthodox Patriarchate of Moscow, Coptic Orthodox Church of Alexandria, Syriac-Orthodox Patriarchate of Antioch and All the East, Serbian Orthodox Patriarchate, Orthodox Church of Romania and Orthodox Church of Albania) and Protestant churches (Anglican Communion, World Lutheran Federation, Ecumenical Council of Churches, World Evangelical Alliance, World Methodist Council, Christian Church (Disciples of Christ) and World Baptist Alliance).