lody accompanying harmonized music, (usually vocal music).

The word _obbligato_ (It. _bound_, or _obliged_) refers to the
fact that this is usually a melody of independent value, so
important that it cannot be omitted in a complete performance.

_Offertory_ (sometimes spelled _offertoire_, or _offertorium_)--a piece
of music played or sung during the taking up of the offering in the
church service. The word is often applied by composers to any short,
simple piece of music (usually for organ) that is suitable for the above
purpose.

_Opus_--work; used by composers to designate the order in which their
compositions were written, as _e.g._, Beethoven, Op. 2, No. 1.

_Orchestration_--the art of writing for the orchestra, this implying an
intimate knowledge of the range, quality, and possibilities of all the
orchestral instruments.

_Ossia_--or else; used most often to call the attention of the performer
to a simpler passage that may be substituted for the original one by a
player whose skill is not equal to the task he is attempting to perform.

_Overture_--(from _overt_--open)--an instrumental prelude to an opera or
oratorio. The older _overtures_ were independent compositions and bore
no particular relation to the work which was to follow, but in modern
music (cf. Wagner, Strauss, etc.), the _overture_ introduces the
principal themes that are to occur in the work itself, and the
introduction thus becomes an integral part of the work as a whole. The
word _overture_ is sometimes applied to independent orchestral
compositions that have no connection with vocal works, as the _Hebrides
Overture_ by Mendelssohn.

_Pizzicato_--plucked. A term found in music for stringed instruments,
and indicating that for the moment the bow is not to be used, the tone
being secured by _plucking_ the string.

_Polacca_--a Polish dance in three-quarter measure.

_Polonaise_--same as _polacca_.

_Postlude_--(lit. after-play)--an organ composition to be played at the
close of a church service.

_Prelude_--(lit. before-play)--an instrumental composition to be played
at the beginning of a church service, or before some larger work (opera,
etc.). The term is also applied to independent piano compositions of
somewhat indefinite form. (Cf. _preludes_ by Chopin, Rachmaninoff, etc.)

_Priere_--a prayer; a term often applied (especially by French
composers) to a quiet, devotional composition for organ.

_Quintole, quintuplet_