A Social Security number (SSN) is a nine-digit number issued by the Social Security Administration (SSA) in the United States. It is used as a unique identifier for individuals in the United States for purposes such as tracking an individual’s earnings, determining eligibility for Social Security benefits, and for tax purposes.

In the United States, SSNs are primarily used for tracking an individual’s work history and earnings, which are then used to determine their eligibility for Social Security retirement, disability, and survivor benefits. The SSA also uses SSNs to help enforce child support obligations, track individuals for wage reporting purposes, and for administration of other federal and state programs.

Eligible individuals who are authorized to work in the United States, including U.S. citizens, permanent residents (green card holders), and certain non-immigrant visa holders, can apply for an SSN. The process of obtaining an SSN typically involves submitting an application along with supporting documentation to a local Social Security office.

It’s important to note that an SSN is personal information and should be protected. It should not be shared with unauthorized individuals or used for purposes other than those intended by the SSA. Misuse of an SSN can lead to identity theft and other serious consequences.