Definition
Immutable means resistant to change. For a blockchain ledger, the term generally describes how accepted history is difficult to alter without overcoming consensus protections or changing the system’s rules. It should not be interpreted as a universal physical impossibility of modification.
Why Records Resist Change
Cryptographic references connect records, making changes detectable. Consensus rules then determine which history participants accept. In proof-of-work systems, rewriting deeper history requires competing with accumulated work. Other protocols establish finality through different mechanisms and assumptions. Hash links alone detect changes; they do not decide which version of history must be followed.
Key Considerations
Recent blocks may be reorganized, and governance or coordinated software changes can affect a network’s accepted state. Application contracts may also include upgrade or administrative permissions even when transaction history remains visible. Immutability does not ensure that an original entry was accurate, private or legally valid. It can make correcting mistakes harder, so data quality and authorization should be checked before information or instructions are recorded.