The Earned Income credit is a credit which is refundable (meaning it can reduce your tax to zero and then result in a refund). It's based on earned income sources. It's generally only for people with children but can be obtained in limited situations for those without children. It's phased out once you meet certain earned income thresholds, so it only applies to those who work and make little money, relatively speaking.
Success is the ability to go from one failure to another with no loss of enthusiasm..W. Churchill