A HYIP is an investment scheme that has existed for decades, also known as a Ponzi scheme or a scheme which promises higher than market returns in a short span of time. A Bitcoin HYIP is one where Bitcoin is used instead of fiat currencies for all transactions involved.
In a HYIP, the operator utilizes the money paid by new investors to provide higher returns to early investors of the program. The aim of such an exuberant payout is to convince probable investors to also allocate their capital. It is said that instead of investing in legitimate businesses, the operator cycles the money until new investors stop coming and the scheme collapses.