To say shortly, Ethereum is blockchain based decentralized open software platform that enables developers to build and deploy decentralized applications.
The project launched in 2014 by Vitalik Buterin, Mihai Alisie, Anthony Di Iorio, and Charles Hoskinson. The main idea behind project was Bitcoin limitations that would not allow to run decentralized applications on it. Ethereum uses Ether - it’s native asset: to run applications, as a payment for mining and transaction fees, and is also a valuable cryptocurrency on markets reaching top in the coinmarketcap rating.
First of all the main purpose of Ethereum blockchain is to run programming code across the blockchain, not to track the ownership of cryptocurrency as it goes in the Bitcoin public ledger.
It is a Turing complete software running on the Ethereum netwrok. Ethereum Virtual Machine is a paltform that enables developers to built thousands of applications running on the decentralized netwrok.
The main purpose of EVM is smart contracts execution.
Smart contracts is a technology created to implement self-executed operations without the need of third-parties called intermediaries. Ethereum's smart contracts are based on different computer languages, which developers use to program their own functionalities.
They contain rules, penalties, and conditions on which the operation will be completed. In the nearest future, the world will see their implementation in absolutely different fields of life. They are fast, cheap, secured and trustless. They can be uploaded to the Ethereum blockchain and each execution will be registered by the whole system of nodes.
Node is a computer connected to the Ethereum Network Full. node means that the computer fully verifies all of the rules of Ethereum. It is a server running on a p2p network, that allow peers to use them to receive updates about the events on the network. It means that they store a lot of data and need a significant upkeep and care.
Every program on Ethereum uses a distinct amount of processing power, and since the program must be run by the nodes, it is important to keep superfluous activity to a minimum. This is why every contract and program on Ethereum is given a cost in “gas.” Gas is a measurement of how much processing power the program will require, and the higher the gas requirement, the more Ether tokens the user will need to spend.
Dapps are applications running on Ethereum Virtual Machine.
They are always open-sourse, autonomous and secured.