A more thorough explanation:

Quadruplicatio is a type of legal pleading used in Roman and civil law. It is the third defensive pleading made by a defendant, following the triplicatio. It is similar to the rebutter used in common law. In old Scots law, it is called quadruply. A plaintiff can also use quadruplicatio as a pleading, following the triplicatio, replicatio, and exceptio.

In a civil case, the defendant may use quadruplicatio as their third defense. For example, if the plaintiff is suing for breach of contract, the defendant may use quadruplicatio to argue that they did not breach the contract and that the plaintiff did not fulfill their obligations under the contract.