In statistics, Numerical characteristics derived from population data is referred to as parameter, while those derived from the sample data are called statistic. When a sample is drawn from a particular population, the statistic of such sample could be used as either a point or interval estimate of the population. However, the estimator derived from the sample in most cases isn't equal to the exact parameter value. When this happens, that is, when population parameter equals the estimate of the sample statistic, then we have an unbiased estimator.
