If you have Medicare and other health insurance (like from a group health plan, retiree coverage, or Medicaid), each type of coverage is called a “payer.” When there’s more than one payer, “coordination of benefits” rules decide who pays first. The “primary payer” pays what it owes on your bills first, and then sends the rest to the “secondary payer” (supplemental payer) to pay. In some rare cases, there may also be a third payer.