美国联邦基金利率（Federal Funds Rate）是指美国同业拆借市场的利率，其最主要的是隔夜拆借利率。这种利率的变动能够敏感地反映银行之间资金的余缺，美联储瞄准并调节同业拆借利率就能直接影响商业银行的资金成本，并且将同业拆借市场的资金余缺传递给工商企业，进而影响消费、投资和国民经济。

https://fred.stlouisfed.org/series/DFF
这个页面里面有解释：
The federal funds rate is the interest rate at which depository institutions trade federal funds (balances held at Federal Reserve Banks) with each other overnight. When a depository institution has surplus balances in its reserve account, it lends to other banks in need of larger balances. In simpler terms, a bank with excess cash, which is often referred to as liquidity, will lend to another bank that needs to quickly raise liquidity. (1) The rate that the borrowing institution pays to the lending institution is determined between the two banks; the weighted average rate for all of these types of negotiations is called the effective federal funds rate.(2) The effective federal funds rate is essentially determined by the market but is influenced by the Federal Reserve through open market operations to reach the federal funds rate target.(2)