Show business is the entertainment industry, including movies, television, popular music, and theater. Your little brother might want to take tap dancing and singing lessons so he can be in show business some day.
When people need an all-encompassing term for the business of entertaining people, they use show business, or sometimes show biz. This typically includes all aspects of the entertainment industry, from business investors to performers to behind-the-scenes technicians. The first known use of this term was in 1850, from the sense of "putting on a show."