The term 'orchestral horn' is a four-letter word, 'TUBA'. The TUBA is a large brass instrument that is the lowest-pitched and largest of the brass instruments. It is often used in orchestras, concert bands, and marching bands. It has a deep, mellow sound and is usually played with a mouthpiece and three or four valves. The TUBA is an essential part of the orchestra, providing a strong bass line and helping to create a full, rich sound.