A sideman is a professional musician who is hired to perform or record with a group of which he or she is not a regular member. They often tour with solo acts as well as bands and jazz ensembles.[1] Sidemen are generally required to be adaptable to many different styles of music, and so able to fit smoothly into the group in which they are currently playing.[2] Often aspiring musicians start out as sidemen, and then move on to develop their own sound, a name, and fans of their own, or go on to form their own groups. Wikipedia.