Bitcoin Cash (BCH) is a cryptocurrency created from a hard fork of Bitcoin. It is meant to have quicker transactions than Bitcoin.
The fork occurred at block 478,559.
At that block the Bitcoin blockchain split. This created two different coins from block 478,559 forward. Bitcoin and Bitcoin Cash.
Despite its origins, Bitcoin Cash should be considered an altcoin for the time being.
Although for all we know Bitcoin Cash become a major player some day, and in fact some have even predicted Bitcoin Cash could become the dominate Bitcoin (in this unlikely case, it would not longer be an altcoin), Bitcoin Cash is not Bitcoin (BTC) and does not have any direct connection to Bitcoin’s value.
With that said, as its own currency, Bitcoin Cash is useful in that it works just like Bitcoin, but has faster transactions due to its increased block size.
NOTE: Unlike some other Bitcoin hard forks, the Bitcoin Core team generally approved of Bitcoin Cash. See: Correcting misinformation on Segwit2x and btc1.
TIP: When a hard fork occurs, two versions a block chain are created. When this happens anyone holding the coin that forks ends up with 1 new coin for each old coin they held (they essentially get “free coins.”). This has driven up the price of Bitcoin since the summer of 2017 due to a string of forks that created Bitcoin Cash and Bitcoin Gold. A new upcoming fork, Segwit2x, is putting even more upward pressure on Bitcoin’s price as of November 16th. With that said, Segwit2x is more controversial than the Bitcoin Cash for, and it is important to be aware of that controversy (see the above Bitcoin Core link).
ADVICE: Keep an eye out for hard forks. Forked coins don’t often hold the value that the original did, but “free coins” is always a plus. With that said, Bitcoin Cash could end up doing very well in its own right. It is already one of the top coins by market cap here in November 2017.