The title Queen Mother refers to the mother of the king, or the reigning monarch. In the Ancient Near East (ANE) the king would have multiple wives, as did David, and as did Solomon. To prevent favoritism, and intrigue, the ANE kings’ mothers were the queens — the Queen Mothers. Typically, the Queen Mother was an intermediary between subjects and the monarch.
We have a biblical example found in 3 Kingdoms (1 Kings) chapter two. King David has died and has named Solomon king. He has been anointed and enthroned to the surprise of David’s eldest son, Adonijah. With Solomon as king, his mother, Bathsheba, is now Queen Mother. In the following pericope, we see Bathsheba’s role and actions as the new Queen Mother:
Now Adonijah the son of Haggith came to Bathsheba the mother of Solomon and bowed down before her… “Now I ask one petition of you. Do not turn away your face.” Bathsheba said to him, “Speak.” Then he said to her, “Speak to King Solomon, for he will not turn his face from you; and let him give me Abishag the Shunammite for a wife.” So Bathsheba said, “Very well, I will speak for you to the king (3 Kingdoms 2: 13, 16 — 18).