Many people don't distinguish between SSI and SSDI, but they are two completely different government programs. Both programs are overseen and managed by the Social Security Administration; however, there are distinct differences between the two.
The main difference between Social Security Disability Insurance (SSDI) and Supplemental Security Income (SSI) is the fact that SSDI is available to workers who have accumulated a sufficient number of work credits, while SSI disability benefits are available to low-income individuals who have either never worked or who have not earned enough work credits to qualify for SSDI. Likewise, the benefits for these two different programs are paid out much differently, depending on how much an individual has earned or not earned, as the case may be.