When William the Conqueror was king of England, he wanted to know how much money he was earning. He gave a decree that all the people in the land had to be part of a survey. After the survey came in, he ordered it to be put in a book so that he could read it.
Another thing that the Domesday book achieved was to monitor everything that peasants owned. This gave the king knowledge about everything that was happening in his kingdom.
If someone refused to provide information for the book, then he or she would be slain by the law enforcer (e.g. a knight). All the records helped the king tax the people according to how much land, animals, and money they had.
The name of the book was Domesday book, which is the Middle English spelling of "Doomsday book". It was called that because it had so much precise info about everyone in the kingdom, similar to what they imagined being the records that God kept about them in heaven.