A fork or accidental fork is a split in the digital recordings, known as the blockchain.
A blockchain is the technology for creating permanent, secure digital recordings. Imagine the blockchain as a book of records where each new page in that book is what is known as a “block”. Blocks are attached to each other making what is known as the blockchain.
There are hundreds of blockchains created by many groups to record all sorts of information. Each blockchain is maintained simultaneously by a network of computers connected by the Internet. Updates to the blockchain are seen immediately and manipulation is extremely difficult, perhaps impossible.
With blockchains, only one recording (block) should be made at a time. However, sometimes two blocks are created at once by two computers, both valid. Because all recordings are shared among the network of computers, one block will reach one group of computers first while the second block will reach the other group of computers. This creates a split in the blockchain record, known as a fork.
Eventually, a computer in the network will build another block on one of the forks and it will grow. The computers always identify the longer fork as the correct one, and so will smoothly switch over, abandoning the shorter one.