Blockchain is the technology which powers Bitcoin, Ethereum, and other cryptocurrencies. It is an immortal, immutable, openly accessible ledger of all transactions which have happened in the network since its inception. Almost every cryptocurrency has its own Blockchain. New transactions are registered and compiled in batches called "blocks" at regular time intervals; the blocks are created via the process called "Bitcoin mining" and added to the end of the "chain" of all the existing blocks, hence the name for the system. Blockchain's existence allows every user to verify the fact that every specific transaction has indeed taken place at a specific moment in time.