In Christian churches the Sunday after Pentecost (the 50th day after Easter) is called the “Feast of the Holy Trinity”. This feast probably started in the 10th century. In 1334 Pope John XXII made it official for the whole church. In the Anglican and Lutheran Churches the weeks that follow The Feast of the Trinity are dated according to how many weeks after Trinity they are (e.g. the 20th Sunday after Trinity). In the Roman liturgy these Sundays are dated “after Pentecoste” (e.g. the 21st Sunday after Pentecoste).