Transactions in blockchains are public by default. A company may not want its past transactions to be a matter of public record, thus solutions to make transactions completely private are important for user adoption. To introduce privacy-preserving transactions, developers in the blockchain ecosystem have offered up many competing solutions with different trade-offs and benefits such as Bulletproofs, Ring Signatures and Zero-knowledge proofs.
The Tezos developer community has been particularly interested in enabling private transactions by implementing a specific type of zero-knowledge proof called zk-SNARKs. An implementation recently being explored uses the same circuits and trusted setup from Zcash's recent "Sapling" upgrade through OCaml bindings to the original Rust libraries. Sapling is based on a near-optimal proof system developer by Jens Groth and the BLS12-381 pairing-friendly elliptic curve and is over an order of magnitude faster than earlier SNARK implementations (read more about Sapling here).
These SNARKs are also much more succint (as little as 144 bytes), which may be useful in the future for the recursive SNARK scaling techniques described in the "Scaling Tezos" blog post from 2017. This approach is also explored by the Mina Protocol and can be implemented to create Tezos sidechains.