Interregnum queen

An 'interregnum queen is a Great Royal Wife' of a previous Egyptian pharaoh, according to a 1932 report. She rules as regent in the place of her son until he reaches the age to assume the role of pharaoh. Officially the son is assumed to be king, de iure, making his mother officially a co-regent.

In practice, the interregnum queen acts as sole ruler. The term may have been the equivalent of the term "King's Mother".