What is the term for the rate that banks charge each other for overnight loans of $1 million or more?

The term for the rate that banks charge each other for overnight loans of $1 million or more is known as the Federal Funds Rate. This rate is a crucial benchmark in the financial system and is set in the market where banks lend reserves to one another, primarily to manage their reserve requirements and liquidity.

When banks have surplus reserves, they may lend excess funds to other banks that need to maintain minimum reserve levels, and the rate at which these transactions occur is called the Federal Funds Rate. It's a key economic indicator as it influences overall interest rates in the economy, affecting things like consumer borrowing costs and economic growth.

The other terms listed refer to different aspects of banking and lending. The discount rate is the interest rate charged by central banks on loans to commercial banks. The broker loan rate generally pertains to the interest rates charged by brokers to borrow stock or cash, and the prime rate is the interest rate that commercial banks charge their most creditworthy customers. These terms do not pertain to the specific interbank lending scenario described in the question, which clarifies why the Federal Funds Rate is the correct response.