hard fork (blockchain)

Definitions

1. A backward-incompatible change to a blockchain's protocol that permanently splits the network into two separate chains. Nodes that don't upgrade follow the old rules on one chain, while updated nodes follow new rules on the other. Notable examples include Bitcoin Cash (from Bitcoin) and Ethereum Classic (from Ethereum).

   In plain English: A permanent split in a blockchain where the community disagrees on rule changes and goes separate ways, like a road that forks into two paths that never rejoin.

   Example: The community couldn't agree on the block size increase, so the hard fork created two competing chains — and two competing communities.

Related Terms

• Fork
• Upstream / Downstream
• soft fork (blockchain)