In essence, the Blockchain is a shared database. Unlike a traditional database, however, there is no central ownership. Instead, data is managed through the consensus of participants in a network, who work together (with the help of cryptography) to decide what gets added, while each participant maintains an identical, full copy of all transactions.
The network can be public (like bitcoin, open to anyone) or private (restricted to certain members). When new information needs to be added, every computer on the network is notified and updates its copy accordingly. The result is an expansive and distributed source of truth — built not from trust, but through cryptographically enforced consensus.
The information stored can be anything: financial transactions, land-title deeds, personal identity, intellectual property, even “smart contracts” (computer code that executes when certain conditions are met).
Yet Blockchain’s most important attribute is its immutability: once something has been added, it is permanent, stored across thousands of computers, and cryptographically locked.
The technical details of how this is done are somewhat complex, but involve public/private key encryption (for anonymity), proof-of-work (for agreement on what gets added to the ledger), longest-chain rule (for resolving conflict), and peer-to-peer communication networks.