Ethereum is a decentralized computing network and dApp development platform. It also uses blockchain technology to retain the integrity of data and the code being run within the network, which is very important since it’s public (interest is public as well).
The cryptocurrency of the Ethereum network is actually called Ether (ETH). However, many members of the crypto community refer the cryptocurrency itself as Ethereum. Ether is inflationary (coin supply in circulation increases in time) and currently needs proof-of-work to validate its transactions. However there are plans to switch to the proof-of-stake consensus protocol.
The value of Ethereum depends mainly on its ability to host dApp development. dApps are applications that are run through a code that’s maintained by multiple entities, or nodes, in different places. You can actually say that the Bitcoin P2P money remittance & payment service is a dApp.
The Ethereum platform also enables the use of smart contracts, which are contracts between two parties that self-execute (through code) when a condition is fulfilled, eliminating the need for third parties. Most, if not all, ICOs use smart contracts in selling their coins.
Ether (ETH) is the official cryptocurrency of the Ethereum platform. Network users use Ether to pay for gas, which is the price of running a code and making a transaction on the platform.
While Ether is the network’s crypto-coin, you can actually issue new, unique tokens on Ethereum.
In line with protecting the network against spam, transaction fees function as DoS protection as it would cost large amount of money to spam the network.
If you already confirmed a mined transaction, there is no way of reversing it. For example, you accidentally sent Ether to a wrong address, there is no way to retrieve it. This means they are lost forever. However, you may overwrite a transaction when it is still in Pending status.
If your transaction is invalid, it will get discarded right way and won’t be mined or confirmed. On the other hand, Smart Contracts interaction allows the transaction to be confirmed even after a Failed transaction.