The free market is defined as the sum of all voluntary transactions. When the government intervenes and forces some transactions and forcibly prohibits others, this is artificial. Interest rates in the U.S. economy are controlled by the U.S. central bank, the Federal Reserve. The Fed is a quasi-government agency with powers bestowed by Congress. It is not part of the free market. Thus, its interest rates are “artificial.”
Through open market operations, the Fed manipulates interest rates. This redistributes wealth to borrowers from the rest of the population. “Borrowers” are, for the most part — in terms of total money borrowed — super wealthy. When the super wealthy take out multimillion-dollar loans, the Federal Reserve System creates the money out of thin air. This makes all existing money worth less, and thus, it is the redistribution of purchasing power: artificial interest rates redistribute wealth.
Socialism and redistribution go hand-in-hand, but normally, socialism implies redistribution from rich to poor. In this case, where the redistribution goes from poor to rich, it can be seen as reverse socialism.
Since purchasing power is redistributed, the effect is similar to direct taxation — but it is less commonly understood. Thus, it is a tax that’s stealth.