hard fork
A major blockchain update that breaks compatibility with older versions of the software.
A hard fork is a significant change to a blockchain’s code that creates a permanent split in the network. When developers implement a hard fork, computers running the old software can no longer recognize transactions and blocks from computers running the new version. Everyone must upgrade to stay on the same network, or the blockchain splits into two separate, incompatible systems.
Hard forks happen when developers want to make fundamental changes—like increasing transaction limits, changing security rules, or reversing past transactions. The term appears in headlines because hard forks are contentious decisions. They require community agreement, and disagreement sometimes leads to a lasting split where both the old and new blockchain continue operating separately. This differs from a soft fork, a backward-compatible update that doesn’t require universal participation.
Written once as a plain-English reference, not as advice. Nothing here is a recommendation to buy or sell anything.