A more thorough explanation:

Books of Sederunt are the official records of the Court of Session in Scots law.

For example, if a case is heard in the Court of Session, all the details of the case, including the judge's decision, are recorded in the Books of Sederunt.

The Books of Sederunt are important because they provide a historical record of the decisions made by the Court of Session. They are also used by lawyers and judges as a reference when making legal arguments or decisions.