Blockchain

Definition

A blockchain is an ordered history organized into blocks that cryptographically refer to earlier blocks. Those links make alterations evident because changing earlier content changes the commitments that later blocks rely on. A functioning blockchain system also needs rules for validating updates and deciding which history participants should follow. The linked structure alone does not provide decentralization, economic security, or accurate information about the outside world. Bitcoin combines it with proof of work and independent transaction validation, while other networks use different mechanisms. Recent history may be reorganized when the applicable consensus rules select another branch. Public records can be inspected, but visibility does not necessarily identify the people controlling addresses. When evaluating a blockchain, useful questions concern who can propose changes, who verifies them, how disagreements are resolved, and what assumptions protect the ledger against manipulation.