What's a pyramid scheme? How do you define one? What attributes does a pyramid scheme have? One could easily ask what's a currency that's backed by nothing, i

What's a pyramid scheme? How do you define one? What attributes does a pyramid scheme have? One could easily ask what's a currency that's backed by nothing, is inflated to oblivion continuously robbing marginalized peoples' life savings, is often used for illegal drug/weapons/sex-trafficking/and worse crimes, is involved in a good percentage of the world's pollution, and that may soon be worth very little?