Blockchain

A blockchain is a type of distributed ledger technology (DLT) that stores data in a chain of blocks, where each block contains a set of transactions and a cryptographic hash of the previous block. This chaining mechanism makes the data virtually immutable — altering any historical block would require recalculating every subsequent block, which is computationally infeasible on a well-secured network. The ledger is maintained across a decentralized network of computers (nodes), meaning no single entity controls the data.

Blockchains achieve consensus — agreement on the state of the ledger — through various mechanisms. Proof-of-work (used by Bitcoin) requires miners to solve computational puzzles, while proof-of-stake (used by Ethereum) requires validators to lock up cryptocurrency as collateral. Other consensus mechanisms include delegated proof-of-stake, proof-of-authority, and proof-of-history. Each offers different trade-offs between decentralization, security, and scalability — often called the "blockchain trilemma."

Beyond cryptocurrencies, blockchain technology has applications in supply chain management, healthcare records, digital identity, voting systems, real estate tokenization, and more. Public blockchains (like Bitcoin and Ethereum) are permissionless and open to anyone, while private or consortium blockchains restrict participation to authorized entities. The technology represents a fundamental shift in how trust is established in digital transactions — from relying on centralized intermediaries to relying on cryptographic proof and distributed consensus.