STARK is a proof system. It uses cutting-edge cryptography to provide polylogarithmic verification resources and proof size, with minimal and post-quantum-secure assumptions.
ZK-STARKs, invented by StarkWare, enforce the integrity and privacy of computations on blockchains, using novel cryptographic proofs and modern algebra. ZK-STARKs allow blockchains to move computations to a single off-chain STARK prover and then verify the integrity of those computations using an on-chain STARK Verifier.