The quality or state of being probable; the extent to which something is likely to happen or be the case.

a probable or the most probable event.

mathematics extent to which an event is likely to occur, measured by the ratio of the favourable cases to the whole number of cases possible.” the area under the curve represents probability”

For the mathematical field of probability specifically rather than a general discussion, see Probability theory. For other uses, see Probability (disambiguation).Not to be confused with Probably.

**Probability** is a measure quantifying the likelihood that events will occur.^{[1]} See glossary of probability and statistics. Probability quantifies as a number between 0 and 1, where, roughly speaking,^{[note 1]} 0 indicates impossibility and 1 indicates certainty.^{[2]}^{[3]} The higher the probability of an event, the more likely it is that the event will occur. A simple example is the tossing of a fair (unbiased) coin. Since the coin is fair, the two outcomes (“heads” and “tails”) are both equally probable; the probability of “heads” equals the probability of “tails”; and since no other outcomes are possible, the probability of either “heads” or “tails” is 1/2 (which could also be written as 0.5 or 50%).

n event that is expected to happen is known as probable event . The extent to which an event is likely to occur is known as probability . Some events occur regularly without fail. i.e. sun rise which is a regular feature of the nature .Other events occur some times or do not occur at all for example the rain fall , which may or may not be received on a particular day . The concept of probability is developed on the basis of such event of uncertainty When an event does not occur at all or when its occurrence is impossible then it is stated that the probability of occurrence of an event is Zero . which is represented as p = 0 . On the other hand , when there is certainty of the occurrence of an event without fail , it is stated that the probability of that event is one i.e. p = 1 . In biological observations however such extreme probabilities ( p =0 , p =1 ) are rare . Most of the occurrence range between impossibility ( p = 0) and certainty ( p =1 ) i.e. the probability of occurrence range form p = 0 to p = 1 . Thus the probability of occurrence of any biological event has a value between 0 to 1

Probability mainly deals with an event which occur or do not occur at all . If a stands for an event to happen ( success , or successful event ) and b for failure in its happening then the probability of happening or success ( p) is p = a / a+b and the probability of its failure ( q) is q = b /a+b

These concepts have been given an axiomatic mathematical formalization in probability theory, which is used widely in such areas of study as mathematics, statistics, finance, gambling, science (in particular physics), artificial intelligence/machine learning, computer science, game theory, and philosophy to, for example, draw inferences about the expected frequency of events. Probability theory is also used to describe the underlying mechanics and regularities of complex systems.^{[4]}