The Federal Funds Rate is the interest rate banks charge each other for overnight loans of reserves. The Federal Reserve doesn't set consumer rates directly — but this one number ripples through nearly every other rate tracked on this site.
Credit card APRs, home equity lines of credit, and adjustable-rate products tend to move closely with the Fed Funds Rate. Fixed mortgage rates are influenced by it but track the 10-year Treasury yield more directly, since a 30-year mortgage is a much longer-dated bet than an overnight loan.
The Fed sets a target range at scheduled FOMC meetings — not continuously. Showing it as a ticking number would imply movement that isn't happening. We show the current range and the date it was last set instead.