In geography, the term “natural hazard” is typically used to refer to something that is hazardous to people but which is not controlled by people.
There are two major aspects to natural hazards. First, they have to be things that are natural and not caused by people. This means that a war would not be a natural hazard. In addition, something that is at least partly natural will not qualify as a natural hazard if it is partly caused by people. An example of this would be acid rain which is, of course, rain but is made acidic by human activity.
Second, they have to be hazardous to human beings. In other words, a volcano that erupts in the middle of the ocean where there are no people is not a natural hazard. Similarly, if a tsunami were to hit the Antarctic coast, it would probably not be a natural hazard.
Natural hazards, then, are things that are natural and which pose a danger to humans. These would include things like Mt. St. Helens, which erupted and harmed human beings. Another example is the recent tsunami in Japan which was clearly not caused by human action but which was devastating to people.