What is Hard Fork?

A hard fork is a software update that is not backwards compatible. In the context of blockchain technology, a hard fork happens when new rules have been introduced into the blockchain code that are not compatible with the rules of the blockchain's previous code. If network nodes do not update their software, they are unable to communicate with nodes that have updated their software. This sometimes results in the blockchain splitting into two networks — one which operates with the old rules and one which operates with the new, updated rules. For example, Bitcoin Cash emerged after a hard fork of the Bitcoin blockchain.