Bitcoin is a digital currency (cryptocurrency). Similar to traditional currencies such as the US dollar, British pound or euro, there are many types of digital currencies. Other popular ones include Ethereum and Dogecoin. Unlike traditional currencies, though, Bitcoin is not backed or controlled by a central financial institution. Instead, it is decentralized. This makes it popular with those who believe that decentralization can lead to financial freedom, but it also makes it extremely volatile—the whim of bitcoin buyers and sellers causing values to rise and fall.