The party to whom the complaint is against is the defendant. This is the physician or health care practitioner in medicolegal cases.
Also known as claimant. In medicolegal cases this is the patient who has initiated the law suit (also known as action).
Case names are usually given with the plaintiff first, as in Plaintiff v. Defendant
In some jurisdictions a lawsuit is started by filing a summons, claim form and/or a complaint — these documents are known as the pleadings and set out the alleged wrongs committed by the defendant or defendants with a demand for relief.
In other jurisdictions the action is started by delivering (serving) these documents directly to the defendant (a "process server" delivers the documents to the defendant); they are only filed with the court subsequently with an affidavit from the process server that they had been given to the defendant(s) according to the rules of civil procedure.
A trial is an event in which parties come together to a dispute present information (in the form of evidence) in a formal setting, usually a court, before a judge, jury, or other designated finder of fact, in order to achieve a resolution to their dispute.