policyholder; insurance policyholder
Formal term used in insurance contexts to refer to the person who holds an insurance policy.
The policyholder must contact the insurance company immediately if an accident occurs.
被保険者 is the insured person (the one covered by the insurance), while 保険契約者 is the policyholder (the one who holds the contract). They can be the same person but are legally distinct roles.
Compound of 保険 (insurance) + 契約 (contract) + 者 (person).