2) A specific type of scam. The operator (often from nigeria) of the scam promises "investors" that their money will be doubled in a certain number of days. The operator depends on the money provided by later investors to pay off his obligations to the earlier investors. This turns out splendidly for the early investors (assuming that it takes off), but later investors get the short end of the stick, as no more people are enrolling. At this point, the operator usually takes the money he has left and runs. This generally sucks for the later investors. Not that I care, because you have to be a total dumbass to enroll in a ponzi scheme anyhow.
Me: Bill, you dumbass. That's not a ponzi scheme.
2) Just great. I just got another one of those get-rich-quick spams. I'm amazed that anyone buys into ponzi schemes.