Senpai and Kōhai

Senpai (先輩^?) and kōhai (後輩^?) are terms applied to the mentor system in wide use in Japanese culture. The senpai is roughly equivalent to the Western concept of a mentor, while kōhai is roughly equivalent to protégé, though they do not imply as strong a relationship as these words mean in the West.

More simply, these may be translated as senior and junior, or as an elder compared with someone younger in the family/company/organization; the terms are used more widely than a true mentor/protégé in the West and are applied to all members of one group that are senior (the senpai) to all the members of another group (the kōhai).

There is usually no average separation in age between a senpai and his or her kōhai.
A junior student will often refer to senior students as "senpai", and alumni will often refer to alumni from earlier classes as "senpai". This holds true particularly if events bring them together later on, such as joining the same company, serving on a board together, or simply being in a club or parent's organization at the same time.

On rare occasions, a younger person may also be considered the senpai of an elder person if circumstances dictate—such as if the elder entered an organization or company at a later time than the younger did.

A kōhai is expected to respect and obey their senpai, and the senpai in turn must guide, protect, and teach their kōhai as best they can. Senpai/kōhai relationships generally last for as long as the two people concerned stay in contact, even if the original context in which the senpai was senior is no longer relevant.

In Japanese martial arts, the term senpai generally refers to senior level students who hold a black belt. They are expected to assist the sensei with younger or less experienced students.