Alleluia

"Alleluia" is the Greek spelling of a Hebrew expression, "Hallelu Yah[weh]," which simply means "praise the Lord." That phrase is found in the Old Testament as a frame around a number of the psalms (Ps. 103-106; 146-150) and in the New Testament in Revelation 19: 1-6. In Christian liturgical use "alleluia" is usually sung in conjunction with one of the Scripture readings as an acclamation (except during Lent). It is also used during Easter and appears as a phrase in many hymns. Some musical settings of "alleluia" are overtly jubilant; for example, George F. Handel's famous "Hallelujah" chorus in The MessiahPsalter Hymnal (see the index of first lines).

Liturgical Use:
As an independent acclamation traditionally with the reading of the gospel, but appropriate at many other times in worship; as a frame around another psalm or hymn, for example Psalm 70 (sing either "alleluia" or "maranatha").

--Psalter Hymnal Handbook, 1987