the inhabitants of the country of which Babylon was the capital
They were so called till the time of the Captivity (2 Kings 25; Isaiah 13:19; 23:13), when, particularly in the book of Daniel (5:30; 9:1), the name began to be used with special reference to a class of learned men ranked with the magicians and astronomers. These men cultivated the ancient Cushite language of the original inhabitants of the land, for they had a “learning” and a “tongue” (1:4) of their own.
The common language of the country at that time had become assimilated to the Semitic dialect, especially through the influence of the Assyrians, and was the language that was used for all civil purposes. The Chaldeans were the learned class, interesting themselves in science and religion, which consisted, like that of the ancient Arabians and Syrians, in the worship of the heavenly bodies.