What is Ethereum?
Ethereum is an open-source, public, blockchain-based distributed ledger featuring smart contract (scripting) functionality. It enables developers to build blockchain applications with business logic that execute in a trustless environment, while leveraging the high availability of the Ethereum network.
Why does it matter?
Because it opens the door to a global financial system where an Internet connection is all you need to access applications, products and services that operate in a trustless manner. Anyone can interact with the Ethereum network and participate in this digital economy, without the need for third parties and without the risk of censorship.
What are Smart Contracts and Decentralized Applications?
While the word "contract" brings to mind legal agreements; in Ethereum "smart contracts" are just pieces of code that run on the blockchain and are guaranteed to produce the same result for everyone who runs them. These can be used to create a wide range of Decentralized Applications (DApps) which can include games, digital collectibles, online-voting systems, financial products and many others.
The term "Smart Contract" was coined by Nick Szabo in the 90's. Szabo used the basic example of a vending machine to describe how real-world contractual obligations can be programmed into software and hardware systems. Everyone who puts the correct amount of coins into the machine can expect to receive a product in exchange. Similarly, on Ethereum, contracts can hold value and unlock it only if specific conditions are met.
The scripting language used by Ethereum is Turing-complete, essentially meaning that the types of DApps users can design is limited only by their programming skills and creativity.