SOFR stands for Secured Overnight Financing Rates.  SOFR is a broad measure of the cost of borrowing overnight collateralized by U.S. Treasury securities.  It is based on observable transactions in the repurchase market.  The Alternative Reference Rate Committee (ARRC), an industry-led group in which the SEC and other departments and agencies of the U.S. government participate, recommended SOFR as the LIBOR replacement rate.