A symphony is a composition for a full orchestra, including all the sections of what is usually called a symphonic orchestra: woodwinds, brass, percussion, and strings.
During the Classical period, a symphony consisted of four movements, although there were exceptions. A symphony may run from approximately 15 minutes, to longer than an hour.
The first movement, in the Classical period, is nearly always written in the sonata form, and comprises the following: an optional slow introduction; an exposition section which traditionally includes two contrasted themes and concludes with a "Repeat" sign; a Development section, in which some of the musical ideas introduced in the Exposition are developed in a variety of modulations; a Recapitulation section which is a slightly changed Exposition; and a Coda, which can be very short or sometimes quite long (as in the first movement of Beethoven's Fifth Symphony).
The second, slow, movement can occur in a free fantasy form, written in a sonata form or as a theme with variations. The second movement of Beethoven's Fifth is based on two themes with variations and a developmental section.
The third movement is usually of a dance-like character. It can be a "Menuet-Trio-Menuet" movement or "Scherzo-Trio-Scherzo" movement. In his Fifth Symphony, Beethoven uses the Scherzo form with slight changes, leading, without pause, to the last movement.
In many symphonies, the last movement is in the Rondo form. But, it can also be based on the sonata form, or on any other form which the composer chooses.
