Go apprentice
An insei is an official student in Japan studying Go, seeking to become a professional player. Insei study at the Nihon Ki-in (Japanese Go Institute), and once a year 3-4 players who qualify in a yearly tournament become professional players. The word "Insei" is also used for graduate school students in Japan. The Korean equivalent term is "Yeon'gusaeng"(Korean: 연구생; Hanja: 硏究生; RR: Yeon(-)gusaeng), read "kenkyūsei" in Japanese.
Asian players are required to become a professional before the age of 18 while studying as insei, but foreigners have the chance up to the age of about 30.
To become an insei, a person requires a professional to sponsor them, and an application to the Nihon Ki-in. There is no official way to contact a professional for sponsorship. While insei, many people live with their professional sponsor, who tutors and supports them. Some insei just visit their professional sponsor several times a week. The professional sponsor acts as a mentor for the insei.