"Probability is a subject that deals with uncertainty. In everyday terminology, probability can be thought of as a numerical measure of the likelihood that a particular event will occur. Probability values are assigned on a scale from 0 to 1, with values near 0 indicating that an event is unlikely to occur and those near 1 indicating that an event is likely to take place. A probability of 0.50 means that an event is equally likely to occur as not to occur." Encyclopædia Britannica, 2004.

"3. Math. As a measurable quantity: The amount of antecedent likelihood of a particular event as measured by the relative frequency of occurrence of events of the same kind in the whole course of experience; estimated by the ratio of the number of successful cases to the whole number of possible cases. Also, used of quantities which are derived logically by inferential or inductive reasoning, when mathematical concepts may be inapplicable or insufficient." Oxford English Dictionary, 2002.

The word probability derives from the Latin probare (to prove, or
to test). Informally, probable is one of several words applied to uncertain events or knowledge, being more or less
interchangeable with likely, risky, hazardous, uncertain, and doubtful, depending on the
context. Chance, odds, and bet are other words expressing similar notions. As with the theory of mechanics which assigns precise definitions to such everyday terms as work and force, so the theory of probability attempts to quantify the notion of probable." Wikipedia, 2005.