A “fork” is a change to the software of the digital currency that creates two separate versions of the blockchain with a shared history.
Forks can be temporary, lasting for a few minutes, or can be a permanent split in the network creating two separate versions of the blockchain. When this happens, two different digital currencies are also created.
Example:
One of the most well-known forks happened in 2017, when Bitcoin split into Bitcoin (BTC) and Bitcoin Cash (BCH). Both share the same transaction history before the split but operate as completely separate networks afterward.