The term 'Instrument Used in Hillbilly Music' can be summarized as the banjo, a five-letter word. The banjo is a stringed instrument that originated in Africa and was brought to the United States by African slaves. It is now commonly associated with American folk music, particularly bluegrass and country music, which are often referred to as 'hillbilly music'. The banjo is typically played with a pick or fingers and has a distinct twangy sound.