What does COB mean?

Coordination of Benefits (COB) must be completed by the subscriber of the
insurance. Please contact your insurance company by calling the phone
number on the back of the insurance card and let the representative know
that you would like to coordinate benefits for your child. This just means
that the insurance is questioning whether the child/family have other active
insurance. They would have usually mailed you a letter/postcard in the mail
with 4 or sometimes 5 quick questions. This “questionnaire” may be
necessary for insurance companies to recognize each other. If there is no
COB on file for one of the insurance companies, claims will be rejected and
sent to self-pay until the issue is resolved.