Definition
A zero-confirmation transaction, often shortened to 0-conf, is a valid Bitcoin transaction that has been broadcast to the network and is visible in node mempools, but has not yet been mined into a block. Because no block has buried it, it carries zero confirmations and is therefore not settled. Wallets typically show the funds as pending, and most explorers display the transaction within seconds of broadcast.
Why 0-conf is convenient but not final
Accepting a payment at zero confirmations lets a buyer and merchant transact instantly, which is attractive for point-of-sale, vending machines, and ATMs where waiting roughly ten minutes for a block is impractical. The trade-off is that an unconfirmed transaction can still be replaced or double-spent before it is mined. A sender could broadcast a conflicting transaction spending the same coins, and if that version confirms first, the original recipient receives nothing.
Mitigating the risk
Merchants reduce 0-conf risk by connecting to many well-peered nodes, watching for conflicting transactions, rejecting payments that signal Replace-by-Fee, and capping the value they accept without a confirmation. None of these measures are consensus rules; they are voluntary heuristics. For higher-value transfers, waiting for one or more confirmations remains the only cryptographic guarantee.
To understand how 0-conf transactions move and settle, see transaction propagation and confirmation time.
In Simple Terms
A zero-confirmation transaction, often shortened to 0-conf, is a valid Bitcoin transaction that has been broadcast to the network and is visible in node mempools,…