Probability is the measure of the likelihood that an event will occur. It is quantified as a number between 0 and 1, where, loosely speaking, 0 indicates impossibility and 1 indicates complete certainty.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