In the practice of Christianity, canonical hours mark the divisions of the day in terms of fixed times of prayer at regular intervals. A book of hours, chiefly a breviary, normally contains a version of, or selection from, such prayers.
In the Roman Rite, canonical hours are also called offices, since they refer to the official set of prayers of the Church, which is known variously as the officium divinum ("divine service" or "divine duty"), and the opus Dei ("work of God"). The current official version of the hours in the Roman Rite of the Catholic Church is called the Liturgy of the Hours (Latin: liturgia horarum) in North America or divine office in Ireland and Britain.
In Anglicanism, they are often known as the daily or divine office, to distinguish them from the other 'offices' of the Church (holy communion, baptism, etc.), which are commonly observed weekly or less often. In the Eastern Orthodox and Byzantine Catholic Churches, the canonical hours may be referred to as the divine services, and the book of hours is called the horologion (Greek: Ὡρολόγιον). Despite numerous small differences in practice according to local custom, the overall order is the same among Byzantine Rite monasteries, although parish and cathedral customs vary rather more so by locale.