BLUE

In statistics, and in particular in estimation theory, "BLUE" is an acronym for Best Linear Unbiased Estimator. This means that given a sample of data, the estimator is a linear combination of this data which measures the right quantity with no systematic errors (unbiased) and is the most efficient (best) because its variance is minimal.

The Gaussâ€"Markov theorem states that for a linear model in which errors obey certain assumptions (they have expectation zero, are uncorrelated and have equal variances), the ordinary least squares estimator is BLUE.