As mentioned, a blockchain is a distributed ledger of transactions implemented as data batched into blocks that use cryptographic validation to link the blocks together. Each block references and identifies the previous block using a hashing function which forms an unbroken chain (i.e., blockchain). A public blockchain is not stored in one central computer.
Nor is it managed by any central entity. Instead, it is distributed and maintained by multiple computers or nodes that compete to validate the newest block entries before the other nodes to gain a reward for doing so. The block validation system is designed to be immutable. That is to say, all transactions old and new are preserved forever with no ability to delete. Anyone on the network can browse via a designated website and see the ledger. This provides a way for all participants to have an up-to-date ledger that reflects the most recent transactions or changes. In this way, blockchain establishes trust, which as we shall see facilitates transactions and brings many cost-saving efficiencies to all types of transactional interactions.
From a technical point of view, the blockchain is a distributed, transparent, immutable, validated, secured, and pseudo-anonymous database existing as multiple nodes such that if 51 percent of the nodes agree then trust of the chain is guaranteed. The blockchain is distributed because a complete copy lives on as many nodes as there are in the system.