1. A set of roles, policies, and procedures used to establish greater trust in the authenticity of a digital certificate and for use in creating, managing, distributing, using, storing, and revoking digital certificates.

Source: Election Terminology Glossary - Draft, National Institute of Standards and Technology (NIST), https://pages.nist.gov/ElectionGlossary/

2. A framework and services for generating, producing, distributing, controlling, accounting for, and revoking (destroying) public key certificates.

3. A framework consisting of standards and services to enable secure, encrypted communication and authentication over potentially insecure networks such as the Internet.

Source: Explore Terms: A Glossary of Common Cybersecurity Terminology, National Initiative for Cybersecurity Careers and Studies (NICCS), https://niccs.us-cert.gov/about-niccs/glossary

4. A software-based system designed to provide confidentiality, integrity, and authenticity in communications; it relies on asymmetric cryptography.

Source: U.S. Cyberspace Solarium Commission, March 2020, https://subscriber.politicopro.com/f/?id=00000170-c638-d8f7-a7f1-f63b33510000