Utsuro was a quasi family-related community from the late Muromachi period to the Azuchi-Momoyama period that organized family members and vassals around the head of the family, called soryo (heir); organizations such as these were seen among Sengoku daimyo (Japanese territorial lord in the Sengoku period) in the Tohoku and Kanto regions.
洞（うつろ）とは、室町時代後期から安土桃山時代にかけて、現在の東北地方及び関東地方の戦国大名に見られた形態で惣領である当主を中心に一族・家臣をまとめた擬似的要素のある族縁共同体のこと。