A more thorough explanation:

Praejuramentum is a term used in history and law to describe a preparatory oath.

When someone takes an oath, they are making a solemn promise to do something or to tell the truth. A praejuramentum is an oath that is taken before another oath. It is a way of preparing someone to take a more important oath later on.

For example, in medieval times, knights would take a praejuramentum before being knighted. This oath would prepare them for the more important oath they would take when they became a knight. Another example is when a witness in court takes a praejuramentum before giving their testimony. This oath prepares them to tell the truth when they take the official oath to tell the truth.

These examples illustrate how a praejuramentum is a preparatory oath that is taken before a more important oath. It is a way of ensuring that the person taking the oath is ready and prepared to make a solemn promise.