Daihi was the empress dowager who was an empress previously. Since Daihi was used for both the wife of a king and the wife of a great king, Daihi in the royal family had the same title as an Empress dowager in the Chinese empire.
As the empress dowager was mother of the Emperor, she held the position during the duration of his reign. The fundamental role of the empress dowager was to keep authority and stability in the royal family, but some of them rose to power by utilizing their title. The most prominent example is Empress dowager Chonhi (貞熹王后), mother of Yejong (King of Dynasty Korea) and Empress dowager Buntei, mother of Menso (King of dynasty Korea).