Key Transparency is a generic, secure way to discover a recipient’s public keys for addressing messages correctly is important. The PGP web-of-trust for encrypted email is just one example: over 20 years after its invention, most people still can’t or wont use it. The goal of Key Transparency was to simplify this process and create infrastructure that allows making it usable by non-experts. The relationship between online personas and public keys should be automatically verifiable and publicly auditable. Users should be able to see all the keys that have been attached to an account, while making any attempt to tamper with the record publicly visible.”]
Source: https://security.googleblog.com/2017/01/security-through-transparency.html