A disaster is a serious problem that happens over a period of time and causes so much harm to people, things, economies, or the environment that the affected community or society cannot handle it on its own. In theory, natural disasters are those caused by natural hazards, whereas human-made disasters are those caused by human hazards. However, in modern times, the divide between natural, human-made or human-accelerated disasters is more and more difficult to draw. In fact, all disasters can be seen as human-made, due to human failure to introduce appropriate emergency management measures.

A natural disaster is the highly harmful impact on a society or community following a natural hazard event. Some examples of natural hazard events include floods, droughts, earthquakes, tropical cyclones, lightning strikes, tsunamis, volcanic activity, wildfires. A natural disaster can cause loss of life or damage property, and typically leaves economic damage in its wake. The severity of the damage depends on the affected population's resilience and on the infrastructure available. Scholars have been saying that the term natural disaster is unsuitable and should be abandoned. Instead, the simpler term disaster could be used, while also specifying the category of hazard. A disaster is a result of a natural or human-made hazard impacting a vulnerable community. It is the combination of the hazard along with exposure of a vulnerable society that results in a disaster.