'Hallel' definitions:

Definition of 'Hallel'

noun

(Judaism) a chant of praise (Psalms 113 through 118) used at Passover and Shabuoth and Sukkoth and Hanukkah and Rosh Hodesh

Hallel praise, the name given to the group of Psalms 113-118, which are preeminently psalms of praise. It is called "The Egyptian Hallel," because it was chanted in the temple whilst the Passover lambs were being slain. It was chanted also on other festival occasions, as at Pentecost, the feast of Tabernacles, and the feast of Dedication. The Levites, standing before the altar, chanted it verse by verse, the people responding by repeating the verses or by intoned hallelujahs. It was also chanted in private families at the feast of Passover. This was probably the hymn which our Saviour and his disciples sung at the conclusion of the Passover supper kept by them in the upper room at Jerusalem (Matt. 26:30; Mark 14:26).
There is also another group called "The Great Hallel," comprehending Psalms 118-136, which was recited on the first evening at the Passover supper and on occasions of great joy.