The trombone is a brass instrument, a variant of the trumpet whose distinguishing characteristic is that the length of the tube in which sound is produced can be altered by means of a slide–a U-shaped telescoping section that recedes into the main body of the tube like a section of a radio antenna. Hence the instrument is colloquially called a slide trombone. The trombone first appears in pictorial representations around 1490, and in the repertoire of the Renaissance and Baroque its most striking appearances came in the works of Venetian composers such as Giovanni Gabrieli and their German followers. The trombone first became part of the symphony orchestra in the late eighteenth century, when it famously appeared in Mozart’s opera Don Giovanni. In the large Romantic orchestra, the trombone was exploited for its tremendous power, its ability to produce, unamplified, loud sounds near the safe endurance limit of the human ear. That power also made the trombone a crucial component of the primarily outdoor-oriented jazz band, and it remains an important solo and ensemble instrument in jazz of various kinds.

A brass instrument is a musical instrument whose sound is produced by sympathetic vibration of air in a tubular resonator in sympathy with the vibration of the player’s lips. Brass instruments are also called labrosones, literally meaning “lip-vibrated instruments”.

There are several factors involved in producing different pitches on a brass instrument: One is alteration of the player’s lip tension (or “embouchure”), and another is air flow. Also, slides (or valves) are used to change the length of the tubing, thus changing the harmonic series presented by the instrument to the player.

The view of most scholars (see organology) is that the term “brass instrument” should be defined by the way the sound is made, as above, and not by whether the instrument is actually made of brass. Thus, as exceptional cases one finds brass instruments made of wood, like the alphorn, the cornett, the serpent and the didgeridoo, while some woodwind instruments are made of brass, like the saxophone.