Fear is a biological response to a threatening situation that a person is not expecting. Fear can be felt over life threatening situations, like a fire. However, fear can also be felt when faced with far safer experiences such as moving to a new city or starting a new job.
The main difference between anxiety and fear is that fear is based in some immediate context which prompts a ‘fight or flight’ reaction from a person. Whereas, anxiety is a far more drawn out ordeal that imbues a sometimes debilitating sense of dread or panic, and usually springs from a concern about the future.
In humans and animals, fear is determined by perception and learning and is therefore labelled as rational or irrational. An example of a rational fear would be a fear of death. Whereas an example of an irrational fear, or phobia, would be a fear of long words.