A fork happens when the blockchain splits into two different blockchains. This usually happens during the upgradation activity when the updated chain and the old chain split into two, and miners continue the activity on the upgraded chain while abandoning the older one.   Forks can be further divided into soft forks and hard forks. A soft fork is one where the nodes that do not upgrade themselves are still able to mine on the newer chain. At the same time, hard fork means that upgradation is mandatory for mining on the new chain.   Apart from that, forks can also be voluntary or controversial. If someone does not align with the vision of the existing blockchain, they can fork it and create a new blockchain. For example, Litecoin is a fork of Bitcoin.