O: The symbol for diminished.

Oblique Motion: Two melodic lines, where one voice remains stationary, while the other moves.

Octave: An interval eight diatonic scale degrees above it. Two notes an octave apart have the same letter name, and form the most consonant interval possible.

Octet: A piece written for eight parts, or the group that performs such a piece.

Oeuvre: (Fr.) opus.

Open Fifth: A triad that does not contain a third, consisting only of a root and a fifth.

Opera: A musical play, usually entirely sung, making use of costumes, staging, props, sets, and dramatic elements. Operas usually consist of two types of musical elements, the aria, which primarily expresses a single idea or theme, and the recitative which advances the story.

Opera Comique: Comic Opera.

Operetta: A light opera.

Opus: "Work". With a number, used to show the order in which the works by a given composer were written or published. Opus numbers are most often used for composers who catalogued their own works.

Oratorio: An operatic work without staging, sets, or elaborate costumes. Usually performed in a more relaxed setting than a formal opera, and usually having a religious theme.

Orchestration: The art of arranging, writing or scoring music for an orchestra.

Ornament: A melodic embellishment, either written or improvised. Types of ornaments included trills, turns, mordents, and grace notes.

Overtone: A tone that is present in the sounding of a fundamental, due to the physics of the production of musical tones.

Overture: The introductory music for an opera, ballet, or oratorio.

Last updated: 3/6/2023