A Merkle Search Tree is a hybrid of:

• Merkle tree (cryptographically linked data via hashes)
• Binary search tree or trie (for efficient key lookup)

Each node in an MST stores a hash of its children (like in a Merkle tree), but data is also ordered by key (like a Search tree). This means:

• You can prove inclusion/exclusion of a key efficiently.
• You can compare and sync subsets of the tree quickly.