A sample statistic is a formula that allows the analyst to compute a number from a sample with the purpose of inference about a given population. For instance, the sample mean and the sample standard deviation.
From a sample of 50 firms in Florida we can calculate the mean annual salary of their CEO's and the sample standard deviation to make inference about the salaries of CEO's in Florida. In this example:
mean = (Sum of 50 CEO's salaries) / 50