Bitcoin Hard Fork
A fork occurs when enacting a new set of rules. A hard fork is a permanent change/divergence in the blockchainA blockchain is a shared digital ledger, or a continually up... More protocol and is not backwards compatible. This means that nodes that haven’t upgraded can’t validate blocks that have been created by upgraded nodes which follow newer consensusConsensus is a mechanism to achieve the necessary agreement ... More rules.
A good example of a BitcoinThe term "Bitcoin" can either refer to Bitcoin the network, ... More hard fork is the one that took place between bitcoin (BTC) and bitcoin cash (BCH), due to the recommended different approaches to scale and process more transactions.
Note: These are non-technical definitions meant for a general audience and should not be used as legal definition