Incident

A violation or imminent threat of violation of computer security policies, acceptable use policies, or standard security practices.
SOURCE: SP 800-61

An occurrence that actually or potentially jeopardizes the confidentiality, integrity, or availability of an information system or the information the system processes, stores, or transmits or that constitutes a violation or imminent threat of violation of security policies, security procedures, or acceptable use policies.
SOURCE: FIPS 200; SP 800-53

An assessed occurrence that actually or potentially jeopardizes the confidentiality, integrity, or availability of an information system; or the information the system processes, stores, or transmits; or that constitutes a violation or imminent threat of violation of security policies, security procedures, or acceptable use policies.
SOURCE: CNSSI-4009