Asynchronous

Asynchronous describes processes or messages that do not run in lockstep, so one party can send something or carry on working without waiting for the other to respond at that moment. Email is asynchronous; a phone call is synchronous. In payments, many systems handle requests asynchronously: a merchant submits a payment and later receives the result through a webhook notification, rather than holding a connection open. In blockchains, nodes spread across the internet see messages with unpredictable delays, so designers distinguish synchronous, partially synchronous and fully asynchronous network models when proving that Byzantine fault tolerant consensus stays safe. Asynchronous designs handle delays well but make it harder to know when a transaction is finished, which is why payment finality rules matter.