SOFR
Also called: Secured Overnight Financing Rate, SOFR rate
SOFR is the Secured Overnight Financing Rate — the cost of borrowing cash overnight against US Treasuries, and LIBOR's replacement. It's built from actual repo transactions worth roughly a trillion dollars a day rather than from bank estimates, which makes it very hard to manipulate. The trade-off is that it's secured and backward-looking, so it carries no bank credit component and spikes when repo markets seize, as in September 2019.
Where this is taught
Definitions are the trailer. These free levels turn SOFR into something you play — one bite-size lesson, with worked examples, a quiz and XP.