Work credits are the measuring stick that the Social Security Administration uses to decide whether you've accrued enough earnings to qualify for benefits. It takes a minimum of 40 work credits to qualify for Social Security retirement benefits. In 2017, you need $1,300 in earnings to qualify for a single credit, and you can earn up to four credits per year.
The amount of earnings required for a quarter of coverage (QC) in 2019 is $1,360. "Quarter of coverage" is a legal term, but you may also see the term "Social Security credit" (or just "credit") used elsewhere. A QC is the basic unit for determining whether a worker is insured under the Social Security program. No matter how high your earnings may be, you can not earn more than 4 QC's in one year.