Probability is the chance that something will happen, there are two kinds of probability, theoretical and experimental. Theoretical probability is based on a sample or repeated trials of the experiment. The experimental probability is given by: 
OR
Theoretical probability:
When all outcomes are equally likely the theoretical probability of an event is the ratio of the number of favorable outcomes to the number of possible outcomes.
In math the definition for probability is: a numerical measure of the likelihood of occurrence of an event. EX. You want to take a blue marble from a bag containing 1 blue marble and 5 red marbles is 1 in 5 or 20%.

PLEASE APPROVE MY ANSWER IF YOU LIKED IT!!