Hallelujah  Halleluyah, or Alleluia, is a transliteration of the Hebrew word הַלְלוּיָהּ meaning "[Let us] praise (הַלְלוּ) God (יָהּ)" (or "Praise (הַלְלוּ) [the] Lord (יָהּ)"). It is found mainly in the book of Psalms. It has been accepted into the English language. The word is used in Judaism as part of the Hallel prayers and has also been adopted by Christianity as a term used to praise God.

Halleluyah is a composite of Hallelu and Yah. It literally translates from Hebrew as "Praise Jah/Yah, [you people!]" or simply "Praise Jah/Yah!" Jah/Yah is the shortened form of the name Jehovah/Yahweh.

The term is used about 24 times in the Hebrew Bible (mainly in the book of Psalms (e.g. 113-118), where it starts and concludes a number of Psalms) and four times in Greek transliteration in Revelation.

 

From http://www.wordiq.com/definition/Hallelujah