A Merkle tree is a binary tree of hashes that enables efficient verification of large data sets, used in blockchains for transaction inclusion proofs.
Leaves are hashes of data chunks; parents hash their children up to a root. Verifiers can check membership with a short proof without downloading the entire set.
"A wallet verifies a transaction is included in a block by checking a Merkle proof against the block header's Merkle root."
"SPV (simplified payment verification) relies on Merkle proofs to verify payments using only block headers."
Merkle trees provide logarithmic proof size and support efficient updates. Variants include Merkle Patricia tries used in account-based chains.
"Proof sizes grow with log2(N); a million leaves need only about 20 sibling hashes."
"Account-based chains use modified trie structures to encode state with verifiable roots."
All terms and definitions may update as the Cryptionary improves.