What does it mean for a transaction to be 'confirmed'?

A transaction is considered 'confirmed' when it has been included in a block and added to the blockchain. This confirmation signifies that the network has recognized the transaction as valid and secure. Once the transaction is incorporated into a block, it becomes part of the permanent, decentralized ledger that comprises the blockchain.

Confirmation serves as an essential aspect of Bitcoin's operation, as it ensures that the transaction has been validated through the consensus of the network. The more confirmations a transaction has—typically indicated by the number of subsequent blocks added after the block containing the transaction—the more secure and irreversible the transaction becomes, mitigating the risk of double-spending or other malicious activities.

In contrast, the other options reflect states that do not imply a transaction's confirmation. For instance, simply initiating a transaction does not guarantee its validity within the network. A rejected transaction indicates that the network has determined it to be invalid, while a non-verified transaction has not undergone the necessary validation process, meaning it is not yet included on the blockchain.