A sackbut is an early form of the trombone used during the Renaissance and Baroque eras. A sackbut has the characteristic telescopic slide of a trombone, used to vary the length of the tube to change pitch, but is distinct from later trombones by its smaller, more cylindrically-proportioned bore, and its less-flared bell. Unlike the earlier slide trumpet from which it evolved, the sackbut possesses a U-shaped slide with two parallel sliding tubes, rather than just one.

The trombone is a musical instrument in the brass family. As with all brass instruments, sound is produced when the player's vibrating lips cause the air column inside the instrument to vibrate. Nearly all trombones use a telescoping slide mechanism to alter the pitch instead of the valves used by other brass instruments. The valve trombone is an exception, using three valves similar to those on a trumpet, and the superbone has valves and a slide.