"Sundays and holy days of obligation are days on which the faithful are obliged to participate in the Mass [... and to] abstain from those works and affairs which hinder the worship to be rendered to God, the joy proper to the Lord's day, or the suitable relaxation of mind and body (Code of Canon Law, Canon 1247).
Holy days mark days in the liturgical year of special importance or that merit special celebration. Worldwide, there is some variation in the dates of celebration of holy days as local Church authorities acknowledge patron saints or allow the celebration of holy days that occur during the week on the nearest Sunday. In England and Wales, according to a 1984 decision of the Bishops' Conference, holy days which fall on Saturday or Monday are in general transferred to the Sunday. From the first Sunday of Advent 2006 the feasts of The Epiphany of the Lord, The Ascension of the Lord and the Body and Blood of Christ (they mean Corpus Christi) have also routinely been transferred to the neighbouring Sunday."