FEMA defines an unmet need as being a deficit between verified disaster-caused damages and obtainable disaster aid, including insurance assistance, Federal and State assistance, and personal resources.
Example: Homeowners Insurance covering Hurricane wind damage but not flood damage and you're not in a flood zone the damage from the flood waters would not be covered by your homeowners insurance so that amount would be unmet.
Example: Your home was completely destroyed and you had to demolish your home and your mortgage company use your insurance money to pay off your loan without offering you options. This is a forced mortgage payoff and the result is you have unmet needs of the total amount of your forced payoff amount to your mortgage.
You were flooded and you had NFIP but not enough to cover the total costs of repairs. You would combine the NFIP insurance for flood with a private bank loan (not SBA or federally secured loans) then the Bank Loan that covered your unmet needs would be an eligible reimbursement by HUD CDBG-DR Grants.
The FEMA Personal Resources mention is typically your retirement or savings. These personal resources may qualify for reimbursement with other federal programs such as the HUD CDBG-DR Grant program. Most states manage this grant program as a reimbursement program which may focus on low-income to moderate-income first then to all income levels if funds are available. Contact your state emergency management or community development people and ask for the agency that manages HUD CDBG-DR Grants.
Follow Disaster Recovery menu links to HUD and State Agency sections for more information about grants.