An oratorio (from the Latin orare " pray ") is the Latin term for a chapel ( within the meaning of prayer house). Chapel-like building are called oratorios, particularly in Latin countries.
The origin of the oratorio is probably due to the fact to build at the shrines of the martyrs for the faithful a chapel to allow them prayer at the place of martyrdom. The oldest surviving oratorio is the Bishop's Chapel in Ravenna, which was built around the year 500. The hl. Benedict uses the term oratory in his Rule, which originated in the 6th century, for the place where the community gathers for prayer. This is usually in the enclosure area or in a side room of the church. Oratories are often lied to like in a gallery of the choir or the nave and have windows to the main room.
The Code of Canon Law (CIC ), the canon law of the Catholic Church, differed in the version of 1917 between different types of oratorios: Private oratorios (the usage only certain people condition, such as a bishop or a family and their guests), semi-public oratories ( the the faithful were open under certain conditions) or public oratories ( which were built for the benefit of all believers ).
The CIC of 1983 does not distinguish between public, semi-public or private oratories. The term oratorio now defines a private place of worship for a group or community that can be made accessible to the faithful at the discretion of the superiors. This definition corresponds to the so-called semi-public oratory from the CIC of 1917. Such oratorios can be built only with the permission of the diocesan bishop, who has previously examined whether the oratorio is " decently equipped ."