A hazard is something that can be dangerous. Fire, Explosives and Fuel are all an example of a hazard Many chemicals can be a hazard. There are ways to get rid of hazardous things. There are different types of hazards; some can catch things on fire; some can burn skin; some can irritate the eyes, etc.
The term 'hazard' is used in driving instruction, and in some traffic-related laws. It simply means 'something a motorist should notice and drive accordingly'. For example, children playing on the pavement (U.S. = sidewalk; Austr. = footpath) are a potential hazard. If any go into the actual road, then they are a real hazard, and motorist should do whatever is safe.