In show business, a guest appearance is the participation of an outsider performer (such as a musician or actor) in an event such as a music record or concert, show, etc. , when the performer does not belong to the regular cast, band or other performing group. In music, such an outside performer is often referred to as a guest artist. In performance art, the terms guest role or guest star are also common, the latter term specifically indicating the guest appearance of a celebrity. The latter is often also credited as special guest star or special musical guest star by some production companies.