1. A set of rules and formats, semantic and syntactic, permitting information systems to exchange information. (NIST Glossary of Information Security Terms – NISTIR 7298 – Revision 2).
Source: NSTAC Report to the President on a Cybersecurity Moonshot, National Security Telecommunications Advisory Committee (NSTAC), https://www.dhs.gov/sites/default/files/publications/NSTAC_CyberMoonshotReport_508c.pdf
2. An agreed upon format for transmitting data between devices.
3. A plan for carrying out a formal or scientific study. Voting system tests are often called protocols.
Source: Information Technology Terminology, U.S. Election Assistance Commission, https://www.eac.gov/documents/2017/09/21/information-technology-terminology-security
4. A set of rules to implement and control some type of association between systems.
Source: U.S. Cyberspace Solarium Commission, March 2020, https://subscriber.politicopro.com/f/?id=00000170-c638-d8f7-a7f1-f63b33510000
5. A set of formal rules describing how to transmit data, especially across a network.
Source: Independent Panel on Internet Voting, British Columbia, https://elections.bc.ca/docs/recommendations-report.pdf