Wikipedia
Gosanke
The , also called simply Gosanke, or even Sanke, were three branches of the Tokugawa clan of Japan descended from clan founder Tokugawa Ieyasu's three youngest sons, Yoshinao, Yorinobu and Yorifusa and allowed to provide a shogun in case of need. The three houses were called Owari House of Tokugawa, Kii House of Tokugawa and Mito House of Tokugawa. However in the Edo Period the term gosanke could also refer to various other combinations of Tokugawa houses, including (1) the shogunal, Owari and Kii houses and (2) the Owari, Kii, and Suruga houses (all with the court position of dainagon). Even after the abolition of the Edo period system of administrative domains (han), the three continue to exist.