The Hebrew “alleluia” means “praise the Lord” or “Praise God.” In the Old Testament this joyful cry appears at the beginning or end of certain psalms, which are considered to have been intended for use in the temple liturgy. The only occurrence of the alleluia in the New Testament appears in the Book of Revelations (19:1-9) where it forms part of the victory hymn sung by the redeemed in heaven.
The Acclamation is linked to the gospel and often accompanied a procession with the gospel usually by a Deacon who has asked the celebrant for a blessing.
Still omitted during Lent, the alleluia is usually replaced by an equivalent acclamation of praise.
General Instruction of the Roman Missal (The Church’s Textbook)
39. …The alleluia or the verse before the gospel may be omitted if not sung.
Music in Catholic Worship
The Memorial Acclamation can be a simple repeated refrain punctuated by Alleluia or in Lent another expression of joy. If incense is used the Book of the Gospel is incensed three times in the name of the Father, Son and Holy Spirit.
We stand as a sign of respect for Christ and the Word of God. The Gospel Acclamation, normally expressive of paschal joy, accompanies the gospel procession. The whole assembly praised Christ who comes to proclaim the good news of salvation.