Assuming this is not an amended return, and you are finished entering all your information and have completed the return in TurboTax, $0 above Federal Refund indicates you do not owe the IRS any money this year. If you owed the IRS, that number would show a negative value.
If you have not yet finished preparing your TurboTax return, this value may change as you continue working through the product, but will be accurate once you finish preparing your return.