What is Social Security?
An insurance program run by the U.S. federal government, that pays monthly benefits to those who have paid into it (or their dependents) and who are unable to support themselves by working.

Social Security's official name is Old Age, Survivors and Disability Insurance (OASDI).

Where does the money for Social Security come from?
Primarily from the Social Security tax, paid by all working people and their employers.

Some additional money comes from interest earned on the Social Security Reserve Fund, and a small amount comes from regular federal income tax on Social Security benefits, paid by some beneficiaries with higher incomes (from sources other than Social Security).