Complex sentence: In statistics, and more specifically in estimation theory, a minimum-variance unbiased estimator (MVUE or MVU estimator) is an unbiased estimator of parameters, whose variance is minimized "for all values of the parameters".
Split into simpler sentences: In statistics, and more specifically in estimation theory, a minimum-variance unbiased estimator (MVUE or MVU estimator) is an estimator of parameters. The MVUE is only valid for unbiased estimators and results when the variance of the estimator is minimized "for all values of the parameters".