A confirmation indicates that a Bitcoin transaction has been added to a block on the blockchain. Once this occurs, every subsequent block adds another confirmation to that transaction, making it increasingly immutable. Typically, a transaction is considered to be fully settled after 6 confirmations.

When a Bitcoin transaction is submitted to the network from a wallet, it is not immediately settled. First, it enters the mempool, where it is considered pending. When miners publish blocks, they take the most profitable transactions with the highest fee-to-data ratio and place them in their block.

When a transaction is included in a block, it is removed from the mempool and considered confirmed. However, this transaction only has one confirmation. It is generally considered a best practice to wait until a transaction has between two and six confirmations before considering it irreversible.

If a transaction only has one confirmation, there is a chance, however small, that the block in which it is included is overwritten and becomes an orphan block. In this rare case, the transaction returns to the mempool and is once again pending. It is not safe to accept a transaction with zero confirmations as payment, as this transaction can be replaced by another transaction which spends the same bitcoin and pays a higher fee.