Definition - What does Successor Beneficiary mean?
A successor beneficiary is the person who receives the death benefit of a life insurance policy in case the primary beneficiary dies first. However, as long as the primary beneficiary lives, they retain the right to the policy proceeds. In case they die after receiving the death benefit, the money goes to their estate, not to the successor.
Insuranceopedia explains Successor Beneficiary
For example, a man names his wife as the primary beneficiary and his brother as a successor beneficiary. If he and his wife were to die in a car accident, his brother would receive the death benefit, but if she survived, the money would go to her, and his brother would have no right to it.