Easton's Bible Dictionary: M. G. Easton, M.A., D.D.
Praise ye Jehovah, frequently rendered "Praise ye the LORD," stands at the beginning of ten of the psalms (Ps. 106, 111:1-113:9, 135, 146:1-150:6), hence called "hallelujah psalms." From its frequent occurrence it grew into a formula of praise. The Greek form of the word (alleluia) is found in Rev. 19:1, 3, 4, 6.