In the context of blockchain, immutability refers to the characteristic that once data has been written to the blockchain, it cannot be altered or deleted. This feature is a fundamental aspect of blockchains and is achieved through the use of cryptographic hash functions and the consensus mechanism. Each block in the chain contains a unique hash of its data, as well as the hash of the previous block, creating an unbreakable link between them. Altering any information in a previous block would require changing all subsequent blocks, which is practically impossible on a decentralized network with widespread consensus. This ensures the integrity and trustworthiness of the blockchain’s history, making it an effective ledger for transactions.