What term refers to an unplanned event that may cause physical harm or property damage?

The term that best describes an unplanned event that may cause physical harm or property damage is "Accident." An accident typically refers to an unexpected event that results in injury or damage. It encompasses scenarios such as vehicle collisions, slips and falls, or any other unforeseen mishap that causes detrimental effects.

The term "incident" is broader and can refer not only to accidents but also to events that might not necessarily result in physical harm or damage but are noteworthy and require attention. While "emergency" denotes a situation that requires immediate action, often related to health and safety, and "occurrence" can refer to any event that happens, it lacks the specific connotation of negative outcomes associated with accidents. Therefore, accident is the most precise choice for describing an unplanned event that can lead to harm or damage.