The term 'relative bassoon' refers to an OBOE, which is a woodwind instrument with four letters. The OBOE is a double reed instrument that produces a mellow and expressive sound. It is often used in orchestras, chamber music, and jazz ensembles. The OBOE is also used in some folk music and popular music genres. The relative bassoon is a larger version of the OBOE, with a deeper and more powerful sound. It is often used in large-scale orchestral works and operas.