What is the meaning of probability?

noun

• A measure of how likely it is that some event will occur; a number expressing the ratio of favorable cases to the whole number of cases possible.
  • usage: "the probability that an unbiased coin will fall with the head up is 0. 5"
  • synonyms: chance
• The quality of being probable; a probable event or the most probable event.
  • usage: "for a while mutiny seemed a probability"; "going by past experience there was a high probability that the visitors were lost"