父母官 Parent official. The Handian dictionary defines it as the old name for the magistrate of a prefecture or county, who could also be called simply “parent.” The Water Margin uses it in the line “in case the parent official asks later.”
The idea goes back to the phrase “parents of the people” in the early classics. Under the Han, people called the official Shao Xinchen “Father Shao” and the official Du Shi “Mother Du.” A saying went: “First there was Father Shao, later Mother Du.”