Probability

From modern epidemiology:

The term probability has multiple meanings. One is that it is the relative frequency of an event. Another is that probability is the tendency, or propensity, of an entity to produce an event. A third meaning is that probability measures someone's degree of certainty that an event will occur. When one says “the probability of death in vehicular accidents when traveling >120 km/h is high,” one means that the proportion of accidents that end with deaths is higher when they involve vehicles traveling >120 km/h than when they involve vehicles traveling at lower speeds (frequency usage), that high-speed accidents have a greater tendency than lower-speed accidents to result in deaths (propensity usage), or that the speaker is more certain that a death will occur in a high-speed accident than in a lower-speed accident (certainty usage).