Long Brass Instrument With a Slide

Word Meaning:

TROMBONE — A musical instrument in the brass family, having a cylindrical bore, and usually a sliding tube (but sometimes piston valves, and rarely both). Most often refers to the tenor trombone, which is the most common type of trombone and has a fundamental tone of B♭ˌ (contra B♭).

Definitions from Wiktionary.