O
Obbligato
Ober
Oblique motion
Oboe
Oboe d'amore
Oboe da caccia
Ocarina
Octatonic Scale
Octave
Octave bass clef
Octave clef
Octave designation
Octave treble clef
Octavo
Octet
Octuple croche
Ode
Oeuvre
Off-beat
Offertory
Office
Officer's Call
Ohne
Old Roman Chant
Oliphant
Ondes Martenot
One hundred and twenty-eighth note
One hundred and twenty-eighth rest
One-line
Op.
Open
Open fifth
Open form
Open roll
Opera
Opera buffa
Opéra comique
Opera seria
Opera-ballet
Operetta
Ophicleide
Opp.
Opus
Oral tradition
Oratorio
Orchestra
Orchestra bells
Orchestration
Ordinary
Organ
Organ point
Organ verset
Organal style
Organistrum
Organology
Organum
Ornament
Ornamentation
Orpharion
Ossia
Ostinato
Ottava
Ottava bassa
Ottava rima
Ottoni
Outer voices
Ouvert
Oval
Overblowing
Overstrung
Overtone
Overture