What is Blockchain?
Last reviewed 2026-05-03
Used by: Bitcoin, NEAR, Aptos, Sui, Canton Network
Entity coverage: 2 protocols, 0 tokens, 8 chains reference this concept.
A blockchain is a replicated append-only ledger maintained by a network of nodes that agree on transaction order via a consensus protocol. Each block cryptographically links to its predecessor, making history tamper-evident.
How it works
A user signs a transaction with their private key and broadcasts it to the peer-to-peer network. Each node checks the signature, nonce, and balance, then holds the transaction in its mempool.
A block producer — a miner under proof-of-work, a selected validator under proof-of-stake — orders pending transactions into a candidate block. The block header commits to two things: the hash of the previous block and a Merkle root summarizing every transaction inside. In proof-of-work the producer must find a nonce whose block hash meets the network's difficulty target; in proof-of-stake the proposer's block is attested to by other validators.
The new block propagates across the network, and every full node independently re-executes its transactions against the protocol rules before appending it and updating its copy of the state — balances and contract storage — deterministically. Because each block embeds its parent's hash, altering an old transaction would change every hash after it and be rejected instantly; as blocks accumulate on top ("confirmations") or a finality gadget votes, reversing history becomes practically impossible.
Why it matters
Blockchains enable trust-minimized transfer of value, agreements, and data without a central operator. They underpin every other term in this glossary.
Real-world examples
Bitcoin (settlement), Ethereum (smart contracts), Solana (high-throughput), Cosmos chains (sovereign apps), Bitcoin L2s (Stacks).
Related terms
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Browse GlossaryFrequently asked questions
What is a blockchain in simple terms?
A blockchain is a replicated append-only ledger maintained by a network of nodes that agree on transaction order via a consensus protocol. Each block cryptographically links to its predecessor, making history tamper-evident.
How does a block get added to a blockchain?
A block producer orders pending transactions into a candidate block, which commits to the hash of the previous block and a Merkle root. The new block propagates across the network, and every full node independently re-executes its transactions before appending it.
What real-world examples of blockchains are mentioned?
Real-world examples include Bitcoin (settlement), Ethereum (smart contracts), Solana (high-throughput), Cosmos chains (sovereign apps), and Bitcoin L2s (Stacks).