An empress that did not meet the conditions of 'lawful wife of an emperor', such as young emperor's Junbo (a woman who was given the status equivalent to the emperor's birth mother) and a wife of retired emperor, was called Kisai no miya.
幼少の天皇の准母、すでに譲位した上皇の妻など「天子の嫡妻」の条件に当てはまらない皇后は皇后宮とされる。