Some think that they define a single rate - namely the overnight lending rate - i.e. the rate at which the banks lend to each other overnight.

In reality, the Fed steers the prevailing interest rates in the economy by explicitly setting the following set of interest rates:

the FED sets a target interest rate range and 4 main explicit interest rates:

1. Overnight Reverse Repo Rate (ON RRP)

2. Interest on Reserve Balances (IORB)

3. Discount Rate - also known as Lending Rate

4. Standing Repo Facility (SRF)

The article explains how each one operates and how together they define a "corridor" for the target federal funds rate.