The official SEC definition:
“A Ponzi scheme is an investment fraud that involves the payment of purported returns to existing investors from funds contributed by new investors. Ponzi scheme organizers often solicit new investors by promising to invest funds in opportunities claimed to generate high returns with little or no risk.”

Gee I guess Mitt Romney was right all along. SS is not a Ponzi scheme. It doesn’t use fraud to bring people in, it just sends them to jail if they refuse to participate.