A "non-refundable" Tax Credit:
A Tax credit that is non-refundable can not be used to increase the amount of your tax refund in any given year.
Non-refundable tax credits are not given back to the holder in the form of a tax refund.
A "refundable" Tax Credit:
If you have qualified for a Refundable tax credit, you have the opportunity to receive that amount as a tax refund, if your payable taxes are less than the tax credit.
If you owe $500 in taxes as part of your annual tax return, but you have qualified for $800 from a refundable tax credit, you would receive a $300 tax refund.