A more thorough explanation:

The confederacy clause is an old legal term that refers to a clause in a complaint that accuses the defendant or defendants of conspiring with others to cheat or harm the plaintiff's personal rights.

For example, if a group of people conspired to steal a person's property, the victim could file a complaint that includes a confederacy clause, accusing all the conspirators of working together to commit the crime.

The confederacy clause is not commonly used in modern legal language, but it was once a common way to accuse multiple defendants of working together to harm the plaintiff.