Fedwire
The US Federal Reserve's system for large interbank payments, where every transfer settles individually and cannot be reversed.
The name gives away the origin. In 1918 the Federal Reserve Banks linked themselves with a private telegraph network so they could move reserves between districts without shipping gold. Computers and terminals replaced the telegraph in the 1970s, but the principle held: Fedwire Funds Service is an RTGS system, and once a payment is booked it is final in central bank money. That is what Americans mean by a "wire transfer", and why a misdirected wire is so hard to get back.
The volumes are absurd: on the order of a quadrillion dollars a year, mostly banks shuffling liquidity and settling securities trades. In July 2025 Fedwire switched its message format to ISO 20022. Small instant payments got their own system, FedNow, in 2023.