Chain Split: Defined in CryptoCurrency

A chain split is a break in the digital recordings, known as blockchain, created by computers running cryptocurrency technology. 

With cryptocurrencies, only one recording (block) should be made at a time. 

However, if the network of users managing cryptocurrency technology disagree on how the blocks should be made, they may split off, each forming their own chain of recordings. This happened with Ethereum in 2016 and now we have Ethereum and Ethereum Classic.