What is Blockchain Technology?

You will see the phrase ‘blockchain technology,’ or commonly just ‘blockchain,’ in many different contexts, and it can be confusing because different people use the words to mean different things.
ETH is the Ethereum blockchain, a reference to the public Ethereum transaction database - but you can also create private Ethereum blockchains by simply running some node software on some
machines and having them connect to each other. Your private Ethereum network will create its own blockchain, and the miners will mine ETH just like in the public network. Your private ETH will not be compatible with the public ETH because your private Ethereum network has a different history from the public version.

All blockchains are distributed ledgers, but you can have distributed ledgers that don’t have blocks of data chained together and broadcast to all participants. Blockchain technologies are the rules or standards for how a ledger is created and maintained. Different technologies have different rules for participation, different network rules, different specifications for how to create transactions, different methods of storing data, and different consensus mechanisms. When a network is created, the blockchain or ledger of record is initially empty of transactions.

Some example blockchain technologies are: Bitcoin, Ethereum, NXT, Corda, Fabric, and Quorum.
Some blockchain technologies operate one way, others operate a slightly different way and you can have multiple instances of any blockchain technology, in separate ledgers.