Ponzi (ponzi scheme) is a fraud activity that the website owner or a person suggests an interest rate to his clients for giving/investing money to him. And he pays previous clicent’s interest with the money from the new investments. So, there appears a pyramid scheme. When new investments does not come, or when there is more people who want to withdraw than invest, the system collapses. As an inevitable ending, the scammer has to run away with the leftover money.
Try to be cautious for ponzi sites while trying to make money online in these type of websites. Do not invest more than you can afford to lose as they will steal your money one day. Even so, if you want to invest by knowing that they will scam you, invest early (max 3 days after launch), and cashout early.