shifting the burden of proof

Definition from Nolo’s Plain-English Law Dictionary

In a lawsuit, the transfer of the obligation to prove particular facts from one party to the other. For example, the person who sued (the plaintiff) initially bears the burden of proving facts that, if no rebutting evidence is presented, would allow that party to win the case. The burden may then shift to the defendant to prove one or more defenses to the plaintiff's case.

Definition provided by Nolo’s Plain-English Law Dictionary.