From the Concise Grove Dictionary of Music:
Oratorio is “an extended musical setting of a sacred, usually non-liturgical, text. Except for a greater emphasis on the chorus throughout much of its history, the forms and styles of oratorio tend to approximate to those of opera in any given period, but the normal manner of performance is without scenery, costumes or action.”

Other well-known oratorios include:
GF Handel
The Messiah
Israel in Egypt
Saul
Solomon
Sampson
JS Bach
St Matthew Passion
Christmas Oratorio
Felix Mendelssohn
Elijah
St. Paul

Find out more:
About Haydn
The first performance