An entity which provides insurance is known as an insurer, insurance company, or insurance carrier. A person or entity who buys insurance is known as an insured or policyholder. The action involves a contract.
The insurance transaction involves the insured assuming a guaranteed and known relatively small loss in the form of payment to the insurer in exchange for the insurer's promise to compensate the insured in case of a covered loss.
The insured receives a contract, called the insurance policy, which details the conditions and circumstances under which the insured will be financially compensated. The amount of money charged is called the premium.