Answer
Success is one of the two outcomes in a binomial probability experiment. This is the outcome that is associated to the probability of success $p$.
Work Step by Step
For example, suppose that the probability that a 75 year old man were to die within one year is 0.17 ($p=0.17$). In this case, success means that a randomly selected 75 year old man died within one year. So, as you can see, in a binomial probability experiment, success does not mean necessarily something positive.
