SSD is another name for Social Security Disability, and is the type of disability benefits most "disabled" individuals seek. The Social Security Administration pays monthly benefits to disabled individuals who have paid into the Social Security system.

SSI is another name for Supplemental Security Income. It is very similar to SSD but the main difference is that you can only have a certain amount of income and assets in order to qualify for SSI. It can be applied for at the same time you apply for SSD benefits.