Some people use the term "ponzi scheme" for any project where the future payments are the primary source of funds for current payments.

In this definition, social security is a ponzi scheme because social security does not invest in anything. All payments are based on the project's ability to take funds from future workers.

Fiat money clearly falls into this category.

Needless to say, most crypto falls into this category.

I like your definition. Something becomes a scheme when the reward structure highly favors the initial investors over future investors.

If a person works at it; they can find a way to frame most investments with the term; so I really think that it is a matter of degree.

!WINE