The term 'Biblical Book Duo' refers to the two books of Kings in the Bible. The books of Kings are part of the Deuteronomistic history, which is a narrative of the history of Israel from the time of Moses to the Babylonian exile. The books of Kings tell the story of the kings of Israel and Judah, including their successes and failures. They also provide insight into the religious and political life of the people of Israel during this period.