Social security is the US federal government Old-Age, Survivors, and Disability Insurance (OASDI) program. Social security provides social welfare and social insurance programs; it is funded through payroll taxes authorized by the Federal Insurance Contribution Act (FICA).
Social security originated in 1935 and has been periodically redefined and realigned since that time. It is one the, if not the, largest governmental program in the world and is the single greatest expense in the federal budget consuming about 41% of the total. Most modern nations offer some type of social security program, though few are as far-reaching (or expensive) as that offered in the US.