'Concubines' in the Bible

When Belshazzar tasted the wine, he gave orders to bring the gold and silver vessels which Nebuchadnezzar his father had taken out of the temple which was in Jerusalem, so that the king and his nobles, his wives and his concubines might drink from them.

Then they brought the gold vessels that had been taken out of the temple, the house of God which was in Jerusalem; and the king and his nobles, his wives and his concubines drank from them.

but you have exalted yourself against the Lord of heaven; and they have brought the vessels of His house before you, and you and your nobles, your wives and your concubines have been drinking wine from them; and you have praised the gods of silver and gold, of bronze, iron, wood and stone, which do not see, hear or understand. But the God in whose hand are your life-breath and all your ways, you have not glorified.