O: The symbol for diminished.
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
Oeuvre: (Fr.) opus.
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
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
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.