According to Coincu, a zero confirmation or unconfirmed transaction is a transaction that has not yet been recorded or verified on the blockchain. To fully understand this concept, it is necessary to have a basic understanding of blockchain technology. A blockchain is a decentralized ledger that consists of a series of blocks. The integrity of the data on the blockchain is maintained by a network of distributed nodes that reach a consensus. In order to manipulate the blockchain, malicious actors would need to control at least 51% of the computing power across the entire network.
When users submit data to the blockchain, they must wait for one of the network's maintainers to register and verify the data before adding it to a block. Each verified block confirms all previous blocks as the blocks are interconnected. A zero confirmation transaction refers to a transaction that has not yet been confirmed on the blockchain and is therefore not part of the blockchain yet. Think of it as a transaction that has been initiated but has not yet been confirmed by the network's miners. Only the party initiating the transaction is aware of it, and until a block is mined and the transaction is confirmed by other network participants, it is considered to have zero confirmation.
It is important to note that the time it takes for a transaction to be confirmed can vary depending on the transaction volume on a specific network. For example, in the case of Bitcoin, a BTC transaction that has been relayed to the nodes in the Bitcoin network but has not yet been included in a block is referred to as a zero confirmation transaction. In certain situations, a zero confirmation transaction can be significant, such as when a seller releases goods before a Bitcoin payment is confirmed by the network, assuming that the confirmation will eventually occur. Typically, at least six confirmations from the network are required to have a reasonable level of certainty that the transaction has been verified.