Graduation (卒業) is a term commonly used in the entertainment industry in Japan. It refers to a young artist's departure after working for some time in a performing group, an entertainment program, an artist management company, etc., and is even used in other industries, such as a model leaving a fashion magazine.
The term is also similarly used in the Sailor Moon musicals. An actor or actress who was leaving the cast was described as "graduating," and their act of leaving the cast was "graduation." During the Senshuuraku performance of their final musical, the graduating cast member was often allowed to perform a special musical number, and was given a farewell during the curtain call.