According to disaster management, the definition of "disaster" is relatively strict. A "disaster" occurs when "hazard" and "vulnerability" exist at the same time. Now global disaster response organizations have different definition for disasters, for example, United Nations considered that a "disaster" should be defined as an event in which at least 10 people died, or at least 100 people injured.

Hazard is one of the factors to cause natural disasters or human-made disasters. It is likely to cause harm or damage to human or environment with sufficient exposure. Potential risk could be divided to the following categories:

• Natural Hazard:
  Earthquakes, typhoons, volcanic eruptions, tsunamis, floods, droughts, tornados, and debris flows.
• Human-made Hazard:
  Wars, genocides, human-induced fire, radioactive wastes, industrial disasters, HIVs, and etc.
• Multi-hazard:
  A hazard causes by nature factors and human-made factors. For example, illegal deforestation may increase the probability of debris flows or landslides being generated in the future.

Vulnerability is the inability to resist a hazard or to respond when a disaster has occurred. Disaster usually causes when vulnerability exists with hazard at the same time. Vulnerability could be divided into following aspects:

• Physical Vulnerability:
  It relates to local environmental and economic conditions, as well as on the quality and state of local buildings and their location with respect to any hazards. For example, people plant the economic crops or build their house on the hillslope would decrease the soil and water conservation over those areas where would easily cause debris flow or landslide during heavy rain or typhoons.
• Social Vulnerability:
  It relates to family, interpersonal relationship and the interaction between communities. For example, if people have good relationship with their neighborhoods or community members, they could support or help residents protect themselves, their families, neighbors, and neighborhoods in an emergency situation.
• Attitude Vulnerability:
  Self-confident provides a positive impact on team emergency response. For example, practice evacuation plan could enhance your abilities to protect yourself and other people when face disasters.

• Natural Forces: climate change, geological deformation, and etc.
• Human Impacts: population characteristic, politic and economy, culture, and etc.
• Physical Environment: buildings, critical infrastructures, public facilities, and etc.

The word is from Greek which means the turning point for better or worse in an acute disease. In Webster’s dictionary, it is explained that it is an unstable or crucial time or state of affairs in which a decisive change is impending.

Could be explained with 3 different meanings：
1. Probability: the possibility of danger
2. Timing: emergency responses when disaster strikes.
3. Turning point: recovery and reconstruction after disasters.