Breaking, or breaking of the blockchain, is the process of splitting up a blockchain into smaller, separate parts. Breaking can be done either intentionally or unintentionally, due to a coding mistake or an attack.
An intentional break of the blockchain occurs when a user or a group of users decide to split the chain into two or more parts. This is done in order to optimize the blockchain and create a more efficient system. The splitting of the chain is done by changing the consensus rules or by introducing a new blockchain protocol. It is important to note that when the chain is broken, it does not necessarily mean that the data stored on the chain is lost.
Breaking of the blockchain can also occur unintentionally, as a result of a coding or programming mistake or an attack. This type of break is known as a “hard fork” and it involves completely splitting the chain into two distinct chains. The chain that was created first is known as the “legacy chain”, while the new chain is known as the “alternative chain”.
Breaking the blockchain can have both positive and negative effects on the blockchain ecosystem. On one hand, a hard fork can create more efficient systems and open up opportunities for developers to experiment with new protocols and technologies. On the other hand, it can also lead to instability in the network, as the two chains may not be able to communicate with each other, or even worse, cause a blockchain split.

Ethereum Classic (ETC) - Ethereum Classic is a cryptocurrency that was created as a result of a hard fork of the Ethereum blockchain in 2016. The fork was initiated after a bug in the DAO (Decentralized Autonomous Organization) smart contract was exploited, leading to the loss of millions of dollars worth of ether.
Bitcoin Cash (BCH) - Bitcoin Cash is a cryptocurrency that was created as a result of a hard fork of the Bitcoin blockchain in 2017. The fork was initiated in order to increase the block size limit from 1MB to 8MB, in order to increase the speed and scalability of the network.
Bitcoin Gold (BTG) - Bitcoin Gold is a cryptocurrency that was created as a result of a hard fork of the Bitcoin blockchain in 2017. The fork was initiated in order to make mining more accessible to individual miners, by changing the mining algorithm from SHA-256 to Equihash, which can be mined using standard GPUs.

Imagine you're playing a game of Jenga, where each block represents a block in a blockchain. When you remove a block, it affects the stability of the whole tower. Similarly, when a block in a blockchain is "broken," it means that the information stored within that block has been altered in some way. This can cause problems with the overall integrity and stability of the blockchain.