Hard fork is a bifurcation of blockchain technology. It is a radical change in a network protocol that validates invalid blocks and transactions that have occurred previously. Hard fork requires all nodes or users to be upgraded to the latest version of the protocol software. Hard fork is the acceptance of new versions of blockchain nodes, older versions; this creates a permanent deviation from the previous version of the blockchain.
Adding a new rule to the code basically creates a fork on the blockchain: one road follows the new, raised blockchain, and the other continues along the old road.
A fork on the blockchain can appear on any cryptocurrency platform, not just bitcoin. Because blockchain and cryptocurrencies work basically the same regardless of the cryptocurrency platform.
We can think of the blocks in the blockchain as cryptographic keys that move the memory. Since the miners in a blockchain set the rules that move memory in the network, these miners set each new rule.