In the context of health insurance and other forms of coverage, coinsurance refers to the percentage of costs that the policyholder is responsible for after they have met their deductible. For instance, if a health insurance policy has a coinsurance rate of 20%, the insured would pay 20% of the medical bills while the insurer covers the remaining 80%. This arrangement ensures that the insured retains a financial stake in their healthcare expenses, which may discourage unnecessary treatments and services.