I remember reading the article a few years ago where the term "natural" ponzi scheme was invented. The author wanted to say that is Bitcoin a Ponzi scheme, but couldn't because it is not. So, they invented the term "natural" ponzi scheme.

A "natural" ponzi scheme is not a ponzi scheme. It more closely resembles a pyramid scheme because both rely on early adopters making money from later adopters, but in a pyramid scheme. Regardless, keep in mind that a "natural" ponzi scheme is an artificial term that doesn't describe any kind of real scam.

A Ponzi scheme is an investment scam in which the operator only pretends to invest the victim's money. They might pay returns using invested money, but they don't necessarily have to. Instead, they may just create account statements that show fake returns. Many restrict withdrawals so that they don't have to pay returns.