What term describes a fixed descriptive measure for an entire population?

A fixed descriptive measure for an entire population is referred to as a parameter. In statistics, a parameter represents a characteristic or measure obtained by using all the data points in a population. It is a definitive value that corresponds directly to the entire group in question.

For example, if you wanted to know the average income of all individuals in a country, that specific average would be a parameter because it applies to the whole population rather than a subset of it. This is distinct from a statistic, which is derived from a sample taken from the population and is subject to variability. The terms coefficient and mean, while related to statistical measures, do not specifically define a comprehensive measure of a population. The mean, specifically, refers to the average of a set of values, which can be calculated as either a parameter or a statistic, depending on whether it pertains to the entire population or just a sample. Thus, the term parameter is most accurately used to describe a fixed descriptive measure for an entire population.