1. Strictly, a mus. setting of a religious lib. for solo singers, ch., and orch., in dramatic form but usually perf. without scenery or costumes in concert-hall or church. The form originated in plays given in the Oratory of S. Philip Neri, Rome, in the mid-16th cent., the mus. form developing c.1600. The first oratorio was Cavalieri's La rappresentazione di anima e di corpo (The Representation of Soul and Body), a morality set to music and perf. in costume. Later oratorios, in concert-form, were written by Carissimi, A. Scarlatti, Schütz, Handel (esp. Messiah, the most popular of all oratorios), Haydn, Spohr, Beethoven, and Mendelssohn (Elijah). Elgar wrote 3 oratorios (but The Dream of Gerontius is not an oratorio).
2. The term is also applied to works similar to these cited above but on a non-religious subject, e.g. Handel's Semele, Tippett's A Child of our Time. Stravinsky's Oedipus Rex is described as an opera-oratorio.
or·a·to·ri·o / ˌôrəˈtôrēˌō; ˌär-/ • n. (pl. -os) a large-scale musical work for orchestra and voices, typically a narrative on a religious theme, performed without the use of costumes, scenery, or action.Well-known examples include Bach's Christmas Oratorio, Handel's Messiah, and Haydn's The Creation.