1. Compromise of security that leads to the accidental or unlawful destruction, loss, alteration, unauthorized disclosure of, or access to, protected information.
Source: The State and Local Election Cybersecurity Playbook, Defending Digital Democracy Project, Harvard Kennedy School Belfer Center for Science and International Affairs, https://www.belfercenter.org/sites/default/files/files/publication/StateLocalPlaybook%201.1.pdf
2. A breach is when information stored on a computer system is unintentionally revealed publically or to some particular party. It can refer to a misconfiguration by which a database permitted access to unintended users or to an actual successful hack by an adversary. In both cases, it may not be clear who has a copy of the breached information.
Source: Election Cybersecurity 101 Field Guide – Glossary, Center for Democracy & Technology, https://cdt.org/insight/election-cybersecurity-101-field-guide-glossary/