Ethereum is a decentralized platform that runs smart contracts: applications that run exactly as programmed without any possibility of fraud or third party interference.
Ethereum is a public blockchain-based platform that uses the cryptocurrency ether to fuel its transactions. Ether is mined by computers around the world and then traded on decentralized exchanges.
The total supply of ether is not capped like Bitcoin, so new ether can be created indefinitely. The current supply of ether as of June 2018 is almost 97 million ETH.
The total supply of ETH will eventually be capped at around 120 million ETH, which is equivalent to about 20% of the total supply of Bitcoin.
The main difference between Ethereum and Bitcoin is that Ethereum can do much more than just being a digital currency. It has the potential to change the way we interact with the internet and how we use apps.
Ethereum can be used to build decentralized apps (dapps) on its blockchain. Dapps are censorship-resistant and no one owns or controls them.
There are currently about 18 million ETH in circulation, and the price of ETH has been on the rise in recent months. If Ethereum becomes widely adopted, its price could continue to rise and there could be a lot more ETH in circulation in the future.