Launched in 2015, Ethereum is the world's programmable blockchain. Like other blockchains, Ethereum has a native cryptocurrency called Ether (ETH). ETH is digital money. People all over the world use ETH to make payments, as a store of value, or as collateral. But unlike other blockchains, Ethereum can do much more.
A block explorer is an online service to track blockchain transactions. It usually is a website where you can see all the new blocks that are being created. You can also search for transactions and wallet addresses. The best-known block explorers are blockchain.info for Bitcoin and etherscan.io for Ethereum.
A smart contract is a computer program or a transaction protocol respectively, which is intended to automatically execute, control or document respectively legally relevant events and actions according to the terms of a contract, of an agreement or of a negotiation.
DAO is an abbreviation of ‘Decentralised Autonomous Organization’. This is basically an organisation that runs automatically on itself without any human interventions. The work is automatically excecuted through Smart contracts.
Blockchain is most simply defined as a decentralized, distributed ledger technology that records the provenance of a digital asset.
A ‘51% attack’ refers to a possible attack on a blockchain by a group of ‘miners’, who hold more than 50% of the hashrate. In such a situation the ‘miners’ have the possibility to deliberately not confirm transactions or to issue transactions twice (double-spend).
