It's basically an investment program where investors are promised high returns but their profit depends on how much money the company makes and more often than not these companies end up losing the money of the investors and they run away and the other times they give out returns at first to increase their trust level and when they have collected enough, they don't invest and just steal the investor's fund and shut down their operations. Which is why it is advised to stay away from HYIP/Ponzi schemes, but people fall for these scams in their greed of earning high returns and end up losing their funds.