Sphere 5.9 - What Are zk-SNARKS?

Zero-Knowledge Succinct Non-Interactive ARgument of Knowledge

The zk-SNARK is the underlying privacy technology for Horizen.
The basic premise is the ability to know that a transaction is true without knowing the details of the transaction.

Here is a good article:
https://cryptodigestnews.com/digital-identity-privacy-and-zero-knowledge-proofs-zk-snarks-3d092b509990