A cornet is a brass musical instrument that looks similar to a trumpet but has a slightly more compact shape and a mellower, warmer sound. Like a trumpet, you play it by buzzing your lips into a mouthpiece and pressing three valves to change notes, but the cornet's tubing is more tightly wound, giving it a rounder tone.

The cornet became extremely popular in the 1800s and early 1900s, especially in military bands, brass bands, and early jazz music. Many famous early jazz musicians, including Louis Armstrong, started on the cornet before switching to trumpet. While trumpets eventually became more common in orchestras and jazz bands because of their brighter, more piercing sound, cornets remain important in British-style brass bands and some concert bands.

If you've ever seen a marching band or heard old recordings of New Orleans jazz, you've probably heard a cornet, even if you didn't realize it. The instrument requires the same breathing techniques and finger patterns as a trumpet, so musicians can often switch between the two, though players say the cornet feels more intimate and more singing in quality.