Cryptocurrencies are peer-to-peer, digital assets that operate on decentralized blockchain networks. Just like the US dollar or other government-issued currencies, you can use cryptocurrencies as a medium of exchange for goods or services on the internet, with growing adoption in offline retail stores around the world. The most commonly cited advantages of cryptocurrencies (over other forms of currency) are their security, privacy, speed, and low cost.
The original cryptocurrency, Bitcoin, was launched in 2009 by a pseudonymous developer named Satoshi Nakamoto, showcasing to the world the first working example of a peer-to-peer, decentralized digital currency. There are now thousands of different cryptocurrencies, yet today Bitcoin is still the largest by market capitalization.