BCH/BTC is a symbol showing the price of Bitcoin Cash (BCH) against Bitcoin (BTC), the most popular cryptocurrency out there, i.e. how much Bitcoin you need to buy one Bitcoin Cash.
Bitcoin Cash, or BCH, is a variety, or fork, of Bitcoin (BTC). The fork was created on Aug 1, 2017, after an unresolved dispute in the miners' communities regarding Bitcoin scaling.
Bitcoin (BTC) is a currency unit used within a payment system with the same name. In Bitcoin environment, clients software runs on multiple computers working together within a single peer-to-peer network, which means every node of the network is independent and self-sufficient.
BTC is a decentralized currency issued by other users who have enough hardware and software resources to support it.
BCH/BTC rate depends entirely on the supply and demand. BCH/BTC price is determined by the popularity of Bitcoin and Bitcoin Cash, its fork.