LIBOR (the London Interbank Offered Rate) was not a traded price. Each morning a panel of banks answered a *survey* question: at what rate could you borrow unsecured from another bank? The answers were trimmed and averaged into a rate for each currency and tenor (overnight, 1-month, 3-month, 6-month, 12-month). Because banks rarely actually borrowed unsecured for three or six months, the inputs were increasingly expert judgement, not transactions. That made the number both manipulable, the 2012 rigging scandal proved traders nudged submissions to profit their own books, and fragile, because it embedded bank credit risk that spikes exactly when markets are stressed.