Definition:
A blockchain is a decentralized, distributed ledger that records transactions across multiple computers so that the record cannot be altered retroactively without the alteration of all subsequent blocks and the consensus of the network.
Key Characteristics:
Decentralization: No single point of control; the network operates on a peer-to-peer basis.

Immutability: Once data is recorded, it cannot be changed without altering all subsequent blocks.

Transparency: All participants can view the entire transaction history.

Security: Cryptographic techniques ensure data integrity and authenticity.

Real-World Analogy:
Imagine a Google Doc shared among multiple users. Everyone has access to the document, and any changes are visible to all. However, once a page is finalized, it becomes read-only, and any alterations require consensus from all users.