A cryptocurrency is a digital or virtual currency that uses cryptography for security. A cryptocurrency is difficult to counterfeit because of this security feature as many cryptocurrencies are decentralized systems based on blockchain technology
Bitcoin was revolutionary because it enabled peer-to-peer payments without requiring trust in either party or a third party like a central bank. Transactions are instead facilitated through the use of blockchain technology.
There are hundreds of different cryptocurrencies and bitcoin alternatives used for all sorts of different applications. Bitcoin continues to be the most popular and currently most useful for everyday transactions
The fundamental structure of how cryptocurrency works applies to both Ethereum and Bitcoin; however, each technology has a different goal. Cryptocurrency is strictly a digital currency and mostly functions as a form of payment. Ethereum takes a different approach, and functions as a platform through which people can use tokens to create and run applications and create smart contracts.