The cornet is a brass instrument similar to the trumpet but distinguished from it by its conical bore, more compact shape, and mellower tone quality. The most common cornet is a transposing instrument in B♭. There is also a soprano cornet in E♭ and cornets in A and C. All are unrelated to the Renaissance and early Baroque cornett.

A brass instrument is a musical instrument that produces sound 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 or labrophones, from Latin and Greek elements meaning 'lip' and 'sound'.