A Jewish ritualistic term to designate Psalms 113-118 (Vulgate 112-117) inclusively, known as the "Hallel of Egypt."
It was chanted in the Feasts of the New Moons, the Feast of the Dedication, the Feast of Weeks, the Feast of Tabernacles, and in the Pasch.
Buxtorf believes that its origin is quite ancient.
Paul of Burgos believes that Christ chanted the Hallel or a part thereof at the Last Supper (Matthew 26).
Some of the later rabbis disturbed the ancient liturgical ordinance by assigning other Psalms, but they do not agree, and their opinions were not adopted.
New Catholic Dictionary