Co-insurance term is usually referred to health insurance companies. In this type of policy, you share the coverage with, the insurance company in percentage of the policy value, after paying deductible or co-payment. It is the split of insurance coverage between you and insurance company; usually the split would be 80/20 % where you are liable to pay 20% and the remaining amount by the insurance company. For example, for health policy you have claimed for $200, according to policy clause you have to pay deductible, let say $100, now after paying deductible the remaining amount is $100, now you have a co-insurance which is split into 80/20%. So you will pay $20 out of $100 from your pocket while the $80 will be paid by co-insurance(meaning the insurance company).