The SWIFT network is the secure, private messaging network run by the cooperative described in the main entry on SWIFT (Society for Worldwide Interbank Financial Telecommunication). More than ten thousand banks, securities firms, market infrastructures and large corporations in most countries connect to it to exchange standardised financial messages.
When people say a payment was sent "over SWIFT", they mean that the payment instruction travelled on this network, typically as an MT103 message through the SWIFT FIN service or as an ISO 20022 message. The network itself does not hold accounts or settle funds. Money moves through accounts that banks hold with each other in correspondent banking, or through payment systems, while SWIFT carries the messages that tell banks what to do.
Participants are identified by a Business Identifier Code, often called a SWIFT code. Beyond payments, the network carries securities, foreign exchange, trade finance and cash management messages, and services such as SWIFT gpi add tracking of payments end to end.