The term 'Xylophone Cousins' refers to two percussion instruments, the xylophone and the marimba. The marimba is a large xylophone-like instrument with wooden bars that are struck with mallets to produce a range of musical tones. It originated in Africa and is now popular in Latin American music. The marimba is often used in orchestras, jazz bands, and other ensembles. It is also a popular solo instrument.