Easy Money
In a general sense, this is just money that's easy to get. Like marrying a billionaire. Or getting elected to Congress.
But there's a more technical definition as well. The Federal Reserve decides monetary policy for the U.S. That means it sets interest rates and generally determines how quickly money moves around in the economy.
The Fed has an "easy money" policy when it keeps rates low and allows cash to move around fairly quickly (the term can apply to any central bank, like the Bank of England or the ECB...we're just using the Fed as an example).
This easy money helps fuel economic growth, because people can get loans relatively cheaply (money's literally easy to get...or at least easier than in a tight money situation.) The downside: it can also fuel inflation.
Because of the inflation risk, the Fed has to keep vigilant that money doesn't get too easy. A fast rise in prices causes its own economic headaches, which is why the Fed tries to follow a not-too-hot-but-not-too-cold Goldilocks policy most of the time.