The sackbut is a historical brass instrument that resembles a trombone but has a narrower bell and a more delicate sound. It was popular during the Renaissance and early Baroque periods, typically made of brass and featuring a slide mechanism for changing pitch. Sackbuts were commonly used in ensembles and orchestras, often playing both sacred and secular music. They are considered ancestors of the modern trombone and are still played today in period music performances, showcasing the rich musical heritage of the time.