Accident: FAA System Safety Definition: An unplanned fortuitous event that results in harm; i.e., loss, fatality, injury, system loss. The specific type and level of harm must be defined; the worst case severity that can be expected as the result of the specific event under study. Various contributory hazards can result in a single accident.
Incident: “An occurrence other than an accident, associated with the operation of an aircraft, which affects or could affect the safety of operations.”