alleluia, an expression of praise to God, occurring in a number of Psalms and in the book of Revelation. It is used extensively in the church rites and ceremonies, usually preceding the Gospel.
Like the term "Amen" (meaning "verily") Alleluia (also spelled Halleluiah and Hallelujah) was adopted into Christian worship in both Eastern and Western churches. Sozomen, the fifth-century historian, states that in A.D. 389 the Christian population of Alexandria sang Alleluia while pulling down a temple of the cult of Serapis.