An occurrence that results in actual or potential jeopardy to 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. See cyber incident. See also event, security-relevant, and intrusion.
Sources:
CNSSI 4009-2015 under incident from FIPS 200 - Adapted

  Occurrence or change of a particular set of circumstances.
Sources:
NIST SP 800-160v1r1 under event from ISO Guide 73

  Anomalous or unexpected event, set of events, condition, or situation at any time during the life cycle of a project, product, service, or system.
Sources:
NIST SP 800-160v1r1 under incident from ISO/IEC/IEEE 15288:2015

  Any observable occurrence in a network or system.
Sources:
CNSSI 4009-2015 under event from NIST SP 800-61 Rev. 2

  Actions taken through the use of an information system or network that result in an actual or potentially adverse effect on an information system, network, and/or the information residing therein. See incident. See also event, security-relevant event, and intrusion.
Sources:
CNSSI 4009-2015

  Any observable occurrence in a network or information system.
Sources:
NIST SP 800-37 Rev. 2 under event from NIST SP 800-61 Rev. 2 - adapted

  Actions taken through the use of an information system or network that result in an actual or potentially adverse effect on an information system, network, and/or the information residing therein.
Sources:
NIST SP 800-160 Vol. 2 Rev. 1 from CNSSI 4009-2015

  An occurrence that actually or imminently jeopardizes, without lawful authority, the confidentiality, integrity, or availability of information or an information system; or constitutes a violation or imminent threat of violation of law, security policies, security procedures, or acceptable use policies.
Sources:
NIST SP 800-171r3 under incident from 44 U.S.C., Sec. 3552
NIST SP 800-172 under incident from 44 U.S.C., Sec. 3552
NIST SP 800-172A under incident from 44 U.S.C., Sec. 3552
NIST SP 800-37 Rev. 2 under incident from 44 U.S.C., Sec. 3552
NIST SP 800-53 Rev. 5 under incident from PL 113-283 (FISMA)

  An occurrence that actually or potentially jeopardizes, without lawful authority, the confidentiality, integrity, or availability of information or an information system; or constitutes a violation or imminent threat of violation of security policies, security procedures, or acceptable use policies.
Sources:
NIST SP 800-128 under incident from 44 U.S.C., Sec. 3552

  Any observable occurrence in a system.
Sources:
NIST SP 800-53 Rev. 5 under event from NIST SP 800-61 Rev. 2 - Adapted