Footnote #1 in our chapter “SRE Cognitive Work” in Blank-Edelman’s Seeking SRE: Conversations about Running Production Systems at Scale:
A note about terms: Use of terms like anomaly, event, incident, and accident tend to evoke strident debates about their exact meanings. They are used inconsistently in tech and elsewhere. Frustration with their variable interpretation has led some to try to give them crisp definitions.
Despite these efforts, none of these terms have fixed meanings. The situation is made even more difficult when word choice has significant consequences. For example, some tech firms have formal processes for handling an incident that do not apply to an event or an anomaly.  (We have witnessed extensive discussions during event response about whether that event meets the organization’s threshold criteria for an incident! Declaring an incident would bring additional resources to bear, generate auditable documentary trails, and involve substantial future work.)
The situation cannot be resolved by fiat. Instead, we need to pay attention to how these terms are used in context and especially to the consequences of the choice of term.
In this chapter, we use the term incident as a pointer to a set of activities, bounded in time, that are related to an undesirable system behavior.
