In the context of blockchain technology, a 'fork' occurs when there is a change in the protocol that is used to maintain the blockchain. This can happen for various reasons, such as the need to fix bugs, to introduce new features, or to fundamentally change how the network operates. There are two types of forks: a hard fork, which is not backwards-compatible and results in the need for nodes to upgrade to the new version, and a soft fork, which is backwards-compatible allowing non-upgraded nodes to still function on the network. Forks can also lead to the creation of new cryptocurrencies, as seen with Bitcoin and Bitcoin Cash.