Orchestral Music

In Ancient Greek theaters, the orchestra was the place in front of the
stage where the chorus would perform, commenting on the events in the
drama. The term as it is used today denotes an large ensemble of
instrumentalists. An orchestra has, at the very minimum, a core group of
string players in which there is more than one player to each part.
Anything smaller is generally categorized as chamber music.

The modern orchestra originated in the early Baroque (around 1600).
Orchestras of string players (and sometimes, in particularly lavish
circumstances, wind and brass players as well) accompanied operas and
other vocal works. By the mid-Baroque (around 1700), composers were
writing for the orchestra as an independent entity.

The symphony was the primary form for orchestral music in the 18th,
19th and early 20th centuries. Haydn, who composed more than 100
symphonies between 1759 and 1795, is justifiably credited with bringing
the form to maturity and expanding the size of the orchestra itself. By the
first decades of the Romantic period, the orchestra had grown to become
a large, varied ensemble that often included harp, contrabassoon, piccolo
and tuba. 20th century composers have written for enormous orchestras
of more than 100 instrumentalists. Many contemporary orchestral works
use pianos, saxophones, vibraphones, exotic percussion and even
electronics in addition to the standard core of instruments.