Jah Jah or Jah is a name for God. It ist the shortform of Jahwe. The Rastafari movement uses this expression often in their songs, there is a Bob Marley Titel "Jah is mighty" and the Reggae Artist Gentleman sings "jah jah mad us and he will see us true". The Rastafari see Haile Selassie of Ethiopia as the incarnation of God and they call him Jah - Jah Rastafari. And so menans Hallelujah: "praise jah".
In the West Indies, the recent high popularity of Christian reggae has led to the often use of the name "Jah" in Christian circles, especially among younger believers and people that like the reggae-dancehall sound. This term is also used in Christian hip hop, typically for no reason but to rhyme, by such artists as KJ-52 and Pigeon John of LA Symphony. P.O.D. has also controversially popularized Rastafarian terms such as "Jah" among young Christians. According to the band, they use such terms to refer to elements of the holy Bible. Songs such as "The Messenjah" from Satellite and "Strength of My Life" from Testify and Matisyahu explicitly use common Rastafarian terms to describe elements of Christianity and Judaism. Matisyahu has also used Rastafarian terminology (also on his album "Shake Off the Dust...Arise"), but never to the same extent.