A hypothesis test formally tests if a population parameter is equal to a hypothesized value. For a binomial distribution, the parameter is the probability of success, commonly referred to as the proportion with the outcome of interest.
The null hypothesis states that the proportion is equal to the hypothesized value, against the alternative hypothesis that it is not equal to (or less than, or greater than) the hypothesized value. When the test p-value is small, you can reject the null hypothesis and conclude the sample is not from a population with the proportion equal to the hypothesized value.
