| Style | Description |
|---|
| Obscuro | Obscuro music (also called outsider music) is not specifically limited to one style, but instead encompasses music that cannot neatly be classified into other genres. |
| Oi! | Oi! is a working class street-level subgenre of punk rock that originated in the United Kingdom in the 1970s. |
| Old school hip hop | Old school hip hop describes the some of earliest hip hop music to come out of the block parties of New York City in the late 1970s and early 1980s. It is preceded by the Roots of hip hop from the early 1970s to the late 1970s, hip-hop formative period. |
| Oldschool Jungle | Oldschool jungle is the name given to a style of electronic music that incorporates influences from genres including breakbeat hardcore, techno, rare groove and reggae/dub/dancehall. |
| Old-time music | Old-time music is a form of North American folk music, with roots in the folk musics of many countries, including England, Scotland and Ireland, as well as the continent of Africa. |
| Olonkho | Yakut epic songs |
| Oltului | Oltului is a type of Romanian folk song, or Doina, sung near the area of the River Olt. Oltului were performed by professional ensembles as part of state-sponsored cultural management efforts during the period of Communist control of Romania. |
| Ondo | Ondo (音頭) is a type of Japanese folk music often heard during Obon festivals. It has a distinct 2/2 rhythm. |
| On ikki muqam | Uyghur classical music suite in 12 parts |
| Opera | Opera is a form of musical and dramatic work in which singers convey the drama. Opera is part of the Western classical music tradition. An opera performance incorporates many of the elements of spoken theatre, such as acting, scenery and costumes and sometimes incorporates dance. |
| Oratorio | An oratorio is a large musical composition including an orchestra, a choir, and soloists. The oratorio was somewhat modeled after the opera. Their similarities include the use of a choir, soloists, an ensemble, various distinguishable characters, and arias. However, opera is musical theatre, while oratorio is strictly a concert piece, though they are sometimes staged as operas. |
| Orchestra | An orchestra is an instrumental ensemble, usually fairly large with string, brass, woodwind sections, and possibly a percussion section as well. The term orchestra derives from the name for the area in front of an ancient Greek stage reserved for the Greek chorus. |
| Organ trio | An organ trio, in a jazz context, is a group of three jazz musicians, typically consisting of a Hammond organ player, a drummer, and either a jazz guitarist or a saxophone player. In some cases the saxophonist will accompany a trio which consists of an organist, guitarist, and drummer, making it a quartet. |
| Organic ambient | Organic ambient music is characterized by integration of electronic, electric, and acoustic musical instruments. Aside from the usual electronic music influences, organic ambient tends to incorporate influences from world music, especially drone instruments and hand percussion. |
| Organica | Organica is a genre music created by SLIPS INTO SPACE in 2007, it is written without predetermining the outcome of the overall sound. |
| Organum | Organum is a technique of singing developed in the Middle Ages, and is an early form of polyphonic music. |
| Oriental metal | Oriental metal is a form of folk metal that incorporates elements of traditional Middle Eastern music. |
| Orovela | eastern Georgian work songs |
| Ottava rima | Ottava rima is a rhyming stanza form of Italian origin. Originally used for long poems on heroic themes, it also came to be popular in the writing of mock-heroic works. Its earliest known use is in the writings of Giovanni Boccaccio. |
| Outlaw country | Outlaw country was a significant trend in country music during the late 1960s and the 1970s (and even into the 1980s in some cases), commonly referred to as The Outlaw Movement (both by fans and by people in the music industry) or simply Outlaw music. |
| Outsider music | Outsider music is music performed either by social outsiders, who have no or few associates in the mainstream music business, or by musicians who choose to live and work in seclusion, often due to compromising behavioral or psychological conditions. |
