Social Security Disability Insurance (SSDI) is a federal program that provides financial assistance to individuals who are unable to work due to a qualifying disability. To be eligible, applicants must have a work history and have paid into the Social Security system through payroll taxes. The program aims to support those who have become disabled and cannot earn a living. To qualify for SSDI, individuals must meet specific medical criteria and demonstrate that their disability significantly impairs their ability to perform basic work activities. Benefits can help cover essential living expenses, providing a safety net for those in need.