A Security Breach is any incident that results in unauthorized access of data, applications, services, networks, and/or devices by bypassing their underlying security mechanisms. A security breach occurs when an individual or an application illegitimately enters a private, confidential, or unauthorized logical IT perimeter.
A security breach is also known as a Security Violation.
Also see Data Breach
Source: https://www.techopedia.com/definition/29060/security-breach