hallel

Hallel
    n 1: (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.