A sax is a shortened, informal name for the saxophone, a musical instrument invented in the 1840s by Belgian instrument maker Adolphe Sax. The saxophone is made of brass and has a curved shape with keys you press to change notes, but it's actually part of the woodwind family because you play it using a reed that vibrates when you blow into the mouthpiece.

Saxophones come in different sizes that play different ranges of notes. The alto sax and tenor sax are the most common. You'll hear the sax in jazz bands, where its smooth, expressive sound can wail, cry, or swing. It's also featured in classical music, marching bands, and rock and roll. When someone says they “play sax” in the school band, they're learning an instrument that can sound mellow and sweet one moment, then bold and brassy the next. The sax became especially famous in jazz music, where players like Charlie Parker and John Coltrane showed how the instrument could express almost any human emotion.