HARD FORK (BLOCKCHAIN)
Hard Fork pertains to a protocol classification that has the capability of validating all transactions that have been previously tagged invalid. Proportionally, it also invalidates all transactions that have been previously determined as valid.
In light of the nature of the Hard Fork protocol, all nodes and users to upgrade to the most recent version of the fork protocol software.
In a Hard Fork, a singular cryptocurrency is split into two permanently. This results into one blockchain that follows the old protocol and the other that follows the latest protocol. The best examples of a Hard Fork are Bitcoin, Bitcoin Cash, Ethereum, and Ethereum Classic.