A more thorough explanation:

A Social Security Number (SSN) is a unique nine-digit number assigned to U.S. citizens, permanent residents, or temporary working residents. The SSN was created in 1936 to keep track of the earnings history of U.S. workers for social security entitlement and benefit computation purposes.

For example, if you work and pay taxes in the United States, you will be assigned an SSN. This number will be used to keep track of your earnings and determine your eligibility for social security benefits when you retire.

Although the social security card was never intended to serve as a personal identification document, the SSN has also become used by many government agencies and other private entities to identify and track a person's financial history.

For example, when you apply for a credit card or a loan, the lender may ask for your SSN to check your credit history and determine your creditworthiness.

The Social Security Administration (SSA) has made the SSN card counterfeit resistant. However, the SSN card is not used as proof of identity because it does not contain personal information about the holder.

An applicant may obtain an SSN and the corresponding card by filling out Form SS-5. A complete list of the required information for the SSN application, such as documentation that proves age, identity, and U.S. citizenship or immigration status, is listed in the Form SS-5. The application and issuance of the SSN card are free of charge for all persons.

The unique nine-digit SSN is composed of three parts:

• The first three digits are the area number. The 3-digit area number is assigned by geographic region.
• The next two digits are the group number, which ranges from 01 to 99 (00 is not used).
• The final four digits are the serial number. The serial number represents a straight numerical series of numbers from 0001–9999 within each group. Serial number 0000 is not assigned.

For example, if your SSN is 123-45-6789, the area number is 123, the group number is 45, and the serial number is 6789.

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