Canonical hours are divisions of time which serve as increments between the prescribed prayers of the daily round. A Book of Hours contains such a set of prayers.

In western Catholicism, canonical hours may also be called offices, since they refer to the official set of prayer of the Roman Catholic Church that is known variously as the Divine Office (from the Latin officium divinum meaning "divine service" or "divine duty"), and the Opus Dei (meaning in Latin, "Work of God"). The current official version of the hours in the Latin Rite of the Roman Catholic Church is called the Liturgy of the Hours (Latin: Liturgia horarum) in North America or Divine Office in the British Isles.

In the Anglican tradition, they are often known as the Daily Office or Divine Office, to distinguish them from the other Offices of the Church.

In the Orthodox Church, the canonical hours may be referred to as the "Divine Services", and the Book of Hours is called the Horologion (Greek: ῾Ωρολόγιον). There are numerous small differences in practice according to local custom; but the overall order is the same among Byzantine Rite monasteries, although parish and cathedral customs vary rather more so by locale.