Zero Confirmation/Unconfirmed Transaction

What Is a Zero Confirmation or Unconfirmed Transaction ?

After sending data to the blockchain, users must wait for one of the modes that maintain the network to register and then verify the data before adding it to a block. As the blocks are connected to one another, each verified block confirms all prior blocks as well. 

A zero confirmation transaction refers to a transaction that has not yet been confirmed on the blockchain and, as such, is not yet part of the blockchain.

You can understand this as a transaction that has already been initiated but has not yet been confirmed by the network’s miners. Only the actor initiating the transaction is aware of it, and until a block is mined and the transaction has been confirmed by other network participants, the transaction is said to have zero confirmation. 

A zero confirmation transaction can be noticeable in certain scenarios, as with a seller who releases their goods before a Bitcoin payment has been confirmed by the network, with the assumption that the confirmation will, over time, actually end up being confirmed. Typically, at least six confirmations from the network are required for it to be fairly certain that the transaction has been verified.