The plaintiff is the one who is suing. They provide evidence and reasoning to why the defendant should be sued. The defendant is the person who is defending themselves for why they should not be sued. They also provide evidence and reasoning. Plaintiff and defendant parties are only in civil cases. Also plaintiffs are always on the left side and defendants are on the right when looking at them in the judges view. (This is irrelevant but I thought I’d tell you, since it helps to determine who is who)