A more thorough explanation:

A COB clause is a provision in an insurance policy that coordinates benefits with other insurance policies. This means that the total amount paid for medical and hospital care will not exceed the benefits available from all sources of insurance combined.

Suppose you have health insurance from your employer and your spouse also has health insurance from their employer. If you have a COB clause in your policy, your insurance company will coordinate benefits with your spouse's insurance company to ensure that you do not receive more than 100% of the cost of your medical expenses. For example, if your medical bill is $1,000 and your insurance covers 80%, your insurance company will pay $800. If your spouse's insurance covers 20%, their insurance company will pay the remaining $200.

Another example is if you have Medicare and also have private health insurance. If you have a COB clause in your private health insurance policy, your private insurance company will coordinate benefits with Medicare to ensure that you do not receive more than 100% of the cost of your medical expenses.

These examples illustrate how a COB clause works to prevent overpayment of medical expenses by coordinating benefits between multiple insurance policies.