Sai Ram. Probability is a specific mathematical chance of a particular event taking place out of all possible outcomes. For example, if a coin is tossed, the probability of a head or a tail turning up is 0.5 each.
Possibility indicates an event that may be improbable. For example, my winning the first prize in a big lottery where lakhs of tickets are sold is very low. So, I can say my winning the first prize is improbable but is not impossible.
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Probability is a way of expressing knowledge or belief that an event will occur or has occurred. In mathematics the concept has been given an exact meaning in probability theory, that is used extensively in such areas of study as mathematics, statistics, finance, gambling, science, and philosophy to draw conclusions about the likelihood of potential events and the underlying mechanics of complex systems.
1 : the condition or fact of being possible
2 : one's utmost power, capacity, or ability
3 : something that is possible
4 : potential or prospective value .