(1) A measurement or a statement about the value of some quantity that is known, believed, or suspected to incorporate some degree of error. (2) The result of applying any estimator to a random sample of data. It is not a random variable but a realization of one, a fixed quantity, and it has no variance although commonly it also furnishes an estimate of what the variance of the estimator is. (Not to be confused with an estimator, which is a prescription for obtaining an estimate.) [L. aestimo, pp. aestimatum, to appraise]