HYIPs(A High Yield Investment Programs) claim to invest in high risk, high yield opportunities. An HYIP can be both offline or online, and maybe be investing in a variety of markets. A large portion of online HYIP's are simply ponzi schemes that call themselves HYIPs. Usually every high yeild program goes with quite a risk, so it will be helpful to use divesification while investing in these programs.
Diversification - the concept of spreading the money among a number of different investments or investment programs in order to reduce risk. It's the idea that one shouldn't put all of your eggs in one basket. Diversification is a good way to reduce your risk and exposure to the market.
Ponzi Scheme. It is any program or claimed investment opportunity which relies on new investments to pay off the older ones. Those whom invest first are thus paid their returns from those who invest after them, leaving the last investors the ones who lose out. Many HYIPs who claim to be trading, investing, etc are really only running a ponzi scheme.