What is "blockchain"

n. A shared record of past transactions in a cryptocurrency network

A blockchain—originally, block chain—is a distributed database that maintains a continuously-growing list of data records secured from tampering and revision. It consists of blocks, holding batches of individual transactions. Each block contains a timestamp and a link to a previous block.

The blockchain is the main technical innovation of bitcoin, where it serves as the public ledger for bitcoin transactions. Every user is allowed to connect to the network, send new transactions to it, verify transactions, and create new blocks, making it permissionless. The bitcoin/blockchain design has been the inspiration for other applications.