Key Definitions: Incident vs. Event
Event (planned event):
Examples: a scheduled nonemergency activity (e.g., sporting event, concert, parade, training exercise, large convention, fair, large gathering, etc.)
Incident (unplanned event):
Examples: An occurrence or event, natural or manmade that requires a response to protect life or property. Incidents can include major disasters, emergencies, terrorist attacks, terrorist threats, civil unrest, wild land and urban fires, floods, hazardous materials spills, nuclear accidents, aircraft accidents, earthquakes, hurricanes, tornadoes, tropical storms, tsunamis, war-related disasters, public health and medical emergencies, and other occurrences requiring an emergency response.
Source: Introduction to the Incident Command System (ICS 100) Student Manual - August 2010, (PDF - 9.0 MB), see glossary. This is part of the National Incident Management System (NIMS).