zk-SNARK

zk-SNARK stands for "zero-knowledge succinct non-interactive argument of knowledge." It's the cryptographic technique that makes Zcash's shielded transactions possible.

In practice, a zk-SNARK lets the Zcash network verify that a shielded transaction is valid — the sender had the funds, no coins were created out of nothing, nothing was double-spent — without learning who sent it, who received it, or how much moved. The proof is "succinct" (small and fast to verify) and "non-interactive" (the prover doesn't need to go back and forth with the verifier).

Zcash was the first major cryptocurrency to use zk-SNARKs in production, starting at its 2016 launch.