In general, Supplemental Security Income (SSI) pays monthly benefits to people who have low income and few resources and are age 65 or older, blind or disabled. To qualify for benefits you must meet the income and assets limits. The definition for disabled is generally th same as for other Social Security disability programs.
For more information on Supplemental Security Income, click the link for the Social Security (SSID) Booklet
or this link for the online version of Understanding Social Security (SSID)