Social Security Number (SSN)
The Social Security number (SSN) is a nine-digit number issued to U.S. citizens, permanent residents, and temporary workers under section 205(c)(2) of the Social Security Act. This number's primary use is to track individual's Social Security accounts. However, the number has over time become the primary individual identification number in the U.S. including for the purpose of filing income tax returns for those who have been employed in the U.S. Once you have received a SSN, by the Social Security Administration (SSA) the number is yours for life, as long as you have the appropriate employment authorization.
The SSN can ONLY be obtained once an individual has a job offer and employment authorization.