zeroconfirmation

Zeroconfirmation refers to a transaction in a blockchain system, such as Bitcoin, that has been broadcast to the network but has not yet been included in a block that has been validated and added to the blockchain. When a transaction is broadcast, it is initially considered to have zero confirmations. Each subsequent block added to the blockchain that includes this transaction increases its confirmation count by one.

The primary implication of a zeroconfirmation transaction is that it is not yet considered immutable or irreversible. While a transaction is in the zeroconfirmation state, there is a theoretical possibility that it could be reversed or altered if it is not successfully included in a valid block. This is because miners can choose which transactions to include in the blocks they create.

For many applications, especially those involving digital currencies, waiting for one or more confirmations is a standard security measure. This waiting period allows the transaction to propagate through the network and be included in a block, making it increasingly difficult and computationally expensive to reverse. However, some services, particularly for small value transactions, may accept zeroconfirmation transactions to speed up the process, accepting a small degree of risk in exchange for immediate finality. This practice is often referred to as "risk-based" or "instant" transactions. The level of trust placed in a zeroconfirmation transaction depends heavily on the specific blockchain's security model and the potential for network attacks like double-spending.