A more thorough explanation:

Proper party

A proper party is a party whose interest may be affected by a judgment, but their presence is not essential for the court to decide the case. They can be added to a lawsuit through a permissive joinder.

In a case where two defendants are jointly and severally liable for negligence, each defendant is a proper party. The plaintiff can sue either of the defendants, but only one is required to be present in court.

Another example could be a case where a person is suing a company for breach of contract. The company's employees may be proper parties because their interests may be affected by the outcome of the case, but their presence is not essential for the court to make a decision.

These examples illustrate that a proper party is someone who has a stake in the outcome of a case, but their presence is not necessary for the court to make a decision. They can be added to the case if needed, but the case can proceed without them.