Refundable Credit
A tax credit that is not limited by the amount of an individual's tax liability. Typically a tax credit only reduces an individual's tax liability to zero. Refundable credits go beyond this and so really can be considered the same as a payment.
Investopedia Commentary
In other words, you'll still get the credit even if you don't owe any tax. The earned income credit is a good example of a refundable credit in the United States.
Related Links
Tax Credit For Plan Expenses Incurred By Small Businesses
The Saver's Tax Credit: an Added Incentive to Fund Your Plan
See also: Adoption Credit, Child Tax Credit, Earned Income Credit, Lifetime Learning Credit, Tax Credit