Cryptographic Accumulator

A primitive that compresses a whole set into one short value and proves an item is (or isn't) in the set with a small proof, without storing the set. Merkle trees are the common example (root + branch); RSA and vector/KZG accumulators give constant-size proofs and native non-membership. They power airdrop allowlists, stateless clients (verkle trees), and privacy nullifier sets.