In the realm of blockchain technology, a hard fork refers to a software update that lacks compatibility with earlier versions. It occurs when new rules are introduced into the code of a blockchain that are incompatible with the rules of its previous code. If network nodes fail to update their software, they become unable to communicate with nodes that have adopted the updated software. Consequently, this can lead to the division of the blockchain into two separate networks—one adhering to the old rules and the other embracing the new, updated rules. For instance, the emergence of Bitcoin Cash followed a hard fork of the Bitcoin blockchain.