or-uh-TOR´-ee-oh
An oratorio is a large-scale cantata with a sacred theme. As such, it’s generally a narrative work (based on scripture) for voices and orchestra, similar to an opera in length, but performed without costumes, scenery, or action.
The world’s most famous oratorio is Messiah (1741), composed by George Frideric Handel (1685-1759). You’ve surely heard the “Hallelujah Chorus” from this work, often performed at Christmas.