Glossary

Obbligato
An Italian term meaning 'obligatory', variously used to describe either an essential part which cannot be missed out, or an optional extra part
Octave
The interval of eight steps, for example from middle C to the next C above it
Octet
A piece of music written for eight players, or the group itself
Opera
A satged drama in which music plays a central role, with soloists singing Arias and Recitatives, and choruses also performing. There is generally very little spoken dialogue. Famous Opera composers include Mozart, Verdi and Wagner
Operetta
Italian for a 'little Opera', Operettas are generally shorter and lighter than Opera, as well as containing more spoken dialogue and often having a comic theme
Opus/Op.
The Latin term used to describe a 'work', generally when referring to the order in which a composer wrote their music or had it published. For example, Beethoven's 20th piece of music would be described as his "Opus 20"
Oratorio
A composition involving solo singers, a chorus and an orchestra, containing arias, recitative and choruses, and covering usually a religious topic. A famous example is Handel's 'Messiah'
Orchestra
A collection of musicians performing together, generally consisting of strings, woodwind, brass and percussion, although there is much variation in exact makeup over history and with different composers and works
Orchestration
The selection of which instruments will play in a given piece of music. Also the practice of re-writing a piece of music for a different choice of instruments
Ornament
Also described variously as a grace note or embellishment, an ornament is an extra note or collection of notes added to a melody to add extra interest. It might be added spontaneously by the performer or written out by the composer. Different types of ornament include trills, mordents, appogiaturas and acciaccaturas
Ossia
An Italian term for an alternative part (perhaps a simpler version of a passage or an ornamented version), usually written above the main stave of music
Ostinato
Italian for 'obstinate', and meaning a persistent figure or rhythm in a piece of music, often repeated continuously throughout an entire work
Overture
An orchestral piece, usually preceding an Opera, Ballet, play or Oratorio, but can sometimes apply to a single-movement orchestral piece in the same style, usually written independently and often used at the beginning of concerts