An accident is a specific, identifiable, unexpected, unusual and unintended external action which occurs in a particular time and place, without apparent or deliberate cause but with marked effects. It implies a generally negative probabilistic outcome which may have been avoided or prevented had circumstances leading up to the accident been recognized, and acted upon, prior to its occurrence.

Narrowly defined, the designation may refer only to the event, while not including the circumstances (facts surrounding) or results of the event; i.e., ‘accident' is constrained to an immediate incident, the occurrence of which results in an unplanned outcome. In common use, however, ‘accident' may include the entire interacting circumstantial framework (chance, pre-existing, or uncontrolled dynamically developing conditions; commonplace actions; random time and place; participants; etc.) leading up to, including, and resulting from, the accident's immediate occurrence.

Physical examples include, e.g., unintended collisions or falls, being injured by touching something sharp, hot, or electrical, or ingesting poison. Non-physical examples are, e.g., unintentionally revealing a secret or otherwise saying something incorrectly, forgetting an appointment, etc.

Experts in the field of injury prevention avoid use of the term 'accident' to describe events that cause injury in an attempt to highlight the predictable and preventable nature of most injuries. Such incidents are viewed from the perspective of epidemiology - predictable and preventable. Preferred words are more descriptive of the event itself, rather than of its unintended nature (e.g., crash, collision, incident, drowning, fall, etc.)

Accidents of particularly common types (auto, fire, etc.) are investigated to identify how to avoid them in the future. This is sometimes called root cause analysis, but does not generally apply to accidents that cannot be deterministically predicted. A root cause of an uncommon and purely random accident may never be identified, and thus future similar accidents remain "accidental."

The informal term "freak accident" typically refers to an unfortunate and improbable event that seems exceedingly unlikely to happen by chance. In extreme contexts, the term may also imply doubt, ambiguity or suspicion about an accident event's cause.

Colloquially considered negative, 'happy' accidents with positive results are also possible.

See also

• Accident proneness
• Air safety
• Accidents and incidents in aviation
• List of aircraft accidents
• Aisles: Safety and regulatory considerations
• Bike
• Bike accident
• Bicycle safety
• Car
• Car accident
• Car safety
• Explosives safety
• List of rail accidents
• List of nuclear accidents
• Risk management
• Sailing ship
• Sailing ship accidents
• Safety
• Safety engineering
• fail-safe
• fail-secure
• Poka-yoke
• Swiss Cheese model
• Tram accident
• Work accident
• Workplace safety
• Material safety data sheet
• Protective clothing
• Occupational health and safety
• Criticality accident
• Accident Analysis