The story
A reference to the Biblical story, related in Exodus chapter 2, in which the baby Moses is abandoned by the river Nile and found by the pharaoh's daughter.
Etymology from Wiktionary, CC BY-SA 4.0.
Baby Moses law
Today it means: A statute that decriminalizes the leaving of (unharmed) infants with certain designated private persons so that they become wards of the state. Full definition →