Refundable Tax Credits
from CBO Recent CBO Publications
The U.S. tax code contains many preferences that lower or eliminate the amount of taxes owed. Those preferences include deductions, exclusions, and tax credits, which can be either refundable or nonrefundable. Refundable tax credits differ from other preferences in a significant way: Whereas other preferences reduce the amount of taxes owed to the government, refundable credits can result in net payments from the government.
http://www.cbo.gov/publication/43767