Burden of proof refers to the duty on a party in a case to submit sufficient evidence on an issue in order to avoid dismissal of the claim. In a criminal trial the burden of proof required of the prosecutor is to prove the guilt of the accused "beyond a reasonable doubt". In a civil trial, the plaintiff must prove their case by a preponderance of the evidence, which translates to a 51% likelihood that all the facts necessary to win a judgment as presented are probably true.
On some issues, the burden of proof may shift to the defendant, such as when the defendant raises a defense which requires affirmative proof by the defendant to defeat plaintiff's claim. If at the close of the plaintiff's presentation he/she has not produced any evidence on a necessary fact the case may be dismissed without the defendant having to put on any evidence.
