An interruption in the functionality of a system. Disruptions may be either internal or external. Internal disruptions may be due to human error, software error, or component failure. External disruptions may be caused by hostile attacks or natural phenomena, such as earthquakes, tsunamis, or hurricanes. Disruptions may also result from loss of resources (external) or from “system” errors, that is, failures caused by the interaction of two or more components that performed as designed (internal).
Jackson,S. (2010) Architecting Resilient Systems: Accident Avoidance and Survival and Recovery from Disruptions, Hoboken, NJ. pp. 39-53
Discussion as to why this is the "consensus" definition for the SEBoK.