What is a hard fork in Bitcoin?

A hard fork in Bitcoin refers to a significant change in the protocol that results in blocks or transactions becoming invalid under the old rules while remaining valid under the new rules. This often occurs when developers or the community decide to incorporate a major change in the blockchain's code, which may enhance functionality, fix issues, or introduce new features.

When a hard fork happens, it creates a divergence in the blockchain, resulting in two separate chains: one that follows the old set of rules and another that adheres to the new protocol. This is different from a soft fork, where backward compatibility is maintained, and nodes running the old version can still participate in the new transactions.

Understanding the implications of a hard fork is crucial for participants in the Bitcoin ecosystem, as it can lead to the creation of a new cryptocurrency, confusion among users, and potentially fragmented support within the community. It signifies a permanent change rather than a mere temporary alteration, which is why choices involving temporary suspensions or security measures do not represent the true nature of a hard fork.