// GLOSSARY -- BLOCKCHAIN & CRYPTO FUNDAMENTALS
What is Merkle Tree?
A Merkle tree is a hierarchical data structure where each leaf contains a data hash and each node contains the hash of its children — enabling efficient verification of large datasets with a single root hash.
WHY IT MATTERS
Merkle trees solve efficient verification: prove a piece of data is in a large set without downloading everything. With log(n) hashes (a Merkle proof), you can verify any element's inclusion.
In blockchains, every block contains a Merkle root of its transactions. Light clients verify transaction inclusion with a few hashes rather than the entire block.
Applications include state management (Ethereum's state trie), airdrop verification (Merkle proofs for claiming), and rollup data availability.
FREQUENTLY ASKED QUESTIONS
How big is a Merkle proof?
O(log n) hashes. For 1 million leaves: ~20 hashes (640 bytes) to prove inclusion. Dramatically smaller than checking all entries.
What are Merkle airdrops?
Token distributions where eligible addresses are in a Merkle tree. Users prove eligibility with a proof, enabling gas-efficient claiming without storing the full list on-chain.
How do Merkle trees relate to rollups?
Rollups post Merkle roots of transaction batches to L1. Anyone can verify a specific transaction was included using a compact proof.