A cryptocurrency is a digital currency designed to work as a medium of exchange. Cryptocurrencies use cryptography to secure and verify transactions, as well as to control the creation of new units. Simply put, cryptocurrencies are entries in a public and distributed database that can only be changed by algorithmic consensus, and they remove the need for trusted third-parties for transaction handling and currency emission. The concept closely resembles peer-to-peer networks for file sharing, with an algorithmic monetary policy on top. If you want to learn more about cryptocurrencies, you should definitely look at videos starring Andreas Antonopoulos. He can make very complex concepts very easy to understand. You may also want to read his recollection of conferences in his book, The Internet of Money, by Merkle Bloom LLC, 2016.
Cryptocurrencies are...