While the French horn is primarily used in classical music pieces, in the mid-20th century it broke into the jazz world. While the instrument remains relatively rare, the role of the French horn in jazz has developed from its beginnings in the 1940s through to the 2010s. Note that the expression "horns" in jazz is often used colloquially to refer to all wind instruments used in jazz (e.g., trumpet, sax, trombone, etc.)