Most of the time I’ve seen something called a Ponzi scheme, there is at least some purported element where earlier investors in an asset make money off of later

Most of the time I’ve seen something called a Ponzi scheme, there is at least some purported element where earlier investors in an asset make money off of later investors in the same asset, without the asset’s true worth actually increasing. That definition isn’t hard to satisfy – it could be something as simple as a stock price becoming overinflated due to hype – and it may even apply to SPACs, but it’s still a more specific requirement than just being fraudulent or unsavory. YMMV.