Definition - What does Adverse Party mean?
The term "adverse party" can simply be defined as the party on the opposite side in a trial.
In a case where there are more than two parties, or there are multiple complaints, then the parties involved can disagree about one or more matters, while being in agreement on other issues.
Justipedia explains Adverse Party
A plaintiff is an adverse party to the defendant. In the same way, a defendant is also an adverse party to the plaintiff.
Beneficiaries of a deceased person, coming together to prove a valid will, while the same two people go against each other on the assets of the deceased, is an example of an adverse party.