A fork in cryptocurrency is a situation where existing rules of the blockchain network are altered and new rules are introduced. This could be done intentionally through a hard fork, or unintentionally through a soft fork. A hard fork is a permanent divergence from the previous version of the blockchain, and requires all nodes and users to upgrade to the latest version of the protocol software. A soft fork is similar to a hard fork but does not require all nodes and users to upgrade. It is backward-compatible, meaning that old nodes will still recognize new blocks produced from the updated version.