Hard fork: Concept

Hard fork, as an event, is a specific form of a fork (a cryptocurrency fork) that arises when the developers of a blockchain decide to make changes to the code so that it will end up with lasting incompatibilities between the older and newer version, breaking the forward compatibility of crypto assets. The new version will no longer be backward-compatible with earlier blocks. As a result, the blockchain divides into two chains: the original blockchain and new version that follows the new set of rules (those defined under the new version).

Hard forking creates an entirely new cryptocurrency, where new coins (such as Bitcoin cash, Bitcoin gold) evolve out of  the original blockchain. Forking occurs for many reasons including addition of functionality, resolving a disagreement as to the direction of evolution, and addressing certain security risks. In other words, hard forks usually result from bugs/ errors in the blockchain or from intentional intervention of the cryptocurrency community.

A hard fork is an event involving a split of a blockchain into two separate blockchains that will function parallel with each other, each under different rules and parameters as to a previous chain. Transaction history and parameters change after the hard fork, where the two networks dissociate from one another after the hard fork, and evolution of each network will not be reflected on the other. Hard forks are major events that lead to modification of a certain characteristic of a project (such as the block size, rewards and hard cap, etc.)

Hard fork as a synonym for Bitcoin Cash

As a result of big discussions held within the bitcoin community about the scalability of the coin, it was decided to introduce Bitcoin Cash as a solution so that more transactions can be processed faster. The bitcoin project was divided (forked)- at the point of split in July 2017- into two: the original currency (bitcoin)- which as left as it was, and the new currency (Bitcoin Cash) that was created as a standalone currency. The new currency has a larger block size that is desgined to allow more transactions to be processed at yet a faster pace. At that moment of splitting, both coins shared the same transaction trail (where owners or holders of bitcoins at the time also owned the same amount of Bitcoin Cash. Thereafter, the new coin started operating on its own blocks and for its own transactions away from the original currency.