A hazard is a source of harm. Hazards are usually categorised in terms of how they cause harm. Many hazards can be found in a situation where they are not causing harm to someone. Hazards may also be necessary for normal work to function, for example, medicines being stored and dispensed in a pharmacy.

The probability of a hazard manifesting into harm and the severity or seriousness of the consequences is defined as risk. This is sometimes defined through the equation: 

An incident arises when a chain of events or scenarios has an unintended consequence, whether harm has occurred or not. A near miss is an incident where harm is averted also known as a ‘no harm incident’.