A person may some confidence or belief regarding the occurrence of some event, Say A. The numerical measure of this confidence is called the subjective probability of the occurrence of A. This probability is based on the experience, intelligence and knowledge of the person who determining the probability in some situation. For example, we may be interested to know whether a certain political system will succeed in a country or not. The probability of success in this situation cannot be determined by objective definitions of probability.
The assessment of this probability is made by some expert. This approach can be applied in real world situations. This probability is subjective in nature. Different persons may have different probabilities for the same situation at the same time.