Definition and background:
The music of the liturgical Christian rite of the Eastern Roman Empire from the establishment of Constantinople (c. 300) until the Ottoman conquest (1453). The Divine Liturgy of the Byzantine rite corresponds to the Mass of the Roman rite.
For more information on the music term "Byzantine rite" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary