This is the party who brings a civil claim. Tort claims are civil claims.The word “Plaintiff” has the same origin as the word “Complaint”. The plaintiff is the one who files a complaint. The complaint in civil litigation is the paper that is filed at the courthouse to initiate litigation.
In criminal litigation there technically is no plaintiff but there is what is called a complaining witness. The complaining witness is typically the victim of the crime but sometimes may be the arresting police officer.
The word “Complaint” can to some people sound a bit harsh. The plaintiff is not literally complaining about anything but rather is seeking some relief for an injury suffered as a result of the alleged behavior or lack thereof by the defendant.
For more information on the word plaintiff see the pages on Wikipedia.