The phrase "unpaid premium" refers to an insurance payment that has not been made by the policyholder. It means that the person has not paid the required amount for their insurance coverage. Full definition
The insured applies to renew his plan within 2 years from the date of first unpaid premium due date. (policybazaar.com)
Grace Period: The insurance company provides an additional period of 30 days from the premium due date for payment of unpaid premium in case of yearly and half - yearly premium payment modes. (policybazaar.com)