Trisagion (Term)
From HymnWiki
The name of the tune refers to a formula of praise addressing God as "thrice holy" or "holy, holy, holy", a formula that has its origin in Isaiah 6:3, which reads "And one [of the six-winged seraphim] cried unto another, and said, Holy, holy, holy, is the LORD of hosts: the whole earth is full of his glory." This was developed by the early churches into a hymn, or prayer, that is generally worded "Holy God, Holy, Mighty, Holy, Immortal, have mercy on us." This "Trisagion" or "Thrice Holy" prayer is a regular part of the Eastern churches' Divine Liturgy, and is also used (particularly on Good Friday) in the Latin Rite.
