In cryptocurrency, "0-conf" (short for zero confirmation) refers to a transaction that has been broadcast to the blockchain network but has not yet been included in a block or received its first confirmation. Although the transaction is visible in the network's mempool and can often be seen in blockchain explorers, it is still considered unconfirmed until miners or validators add it to the blockchain.

Zero-confirmation transactions are popular for situations where speed is more important than absolute security. For example, some retailers, coffee shops, or small online merchants may accept a 0-conf payment because waiting for one or more confirmations could take several minutes or longer. This allows customers to complete purchases almost instantly, improving the payment experience.

However, 0-conf transactions carry additional risk. Since the transaction has not been permanently recorded on the blockchain, it may be vulnerable to issues such as double-spending attacks, where a malicious user attempts to send the same cryptocurrency to another address before the original transaction is confirmed. Features such as Replace-by-Fee (RBF) on some blockchains can also allow an unconfirmed transaction to be replaced with another transaction offering a higher network fee.

For this reason, most cryptocurrency exchanges and businesses require at least one confirmation—and often several confirmations—before considering a transaction final. High-value transfers typically require more confirmations because each additional confirmation significantly reduces the likelihood of reversal through blockchain reorganizations.

In summary, a 0-conf transaction provides fast payment processing but comes with greater security risks than confirmed transactions. It is generally best suited for low-value payments where convenience outweighs the relatively small risk of transaction replacement or double spending.