Senpai and kōhai are an essential element of Japanese seniority-based status relationships, similar to the way that family and other relationships are decided based on age, with even twins being divided into elder and younger sibling. Senpai is roughly equivalent to the western concept of "mentor", while kōhai is roughly equivalent to "protege". Or simply an "elder" vs. someone younger in the family/company/organization—the terms are used more widely than a true mentor/protege in the West. There is usually no average separation in age between senpai and his/her kōhai.