When an insured gives the insurer the right to recover from a third party is called

Waiver is the voluntary relinquishment of a known right, often pertaining to the insurer's ability to enforce a policy provision. It does not involve the transfer of recovery rights to the insurer from the insured, thus failing to address the insurer's right to pursue third parties for reimbursement of claims paid.

Estoppel refers to a legal principle that prevents a party from arguing something contrary to a claim made or implied by their previous actions or statements. While it can be related to insurance policies, it does not specifically address the insurer's right to recover from a third party, making it irrelevant to the concept in question.

Assignment of loss involves transferring rights or interests in a claim or policy from one party to another. However, this term does not specifically capture the insurer's right to pursue recovery from third parties, as subrogation does, which is a more precise legal mechanism focused on recovery actions.