An accent mark placed above variables to indicate averaging, mean values, or complex conjugation in statistics and analysis.
Examples
Sample mean notation
\bar{y} = \frac{1}{n}\sum_{i=1}^n y_i
Complex conjugate of variable y
z = y + i\bar{y}
Average value in statistics
\text{Standard Error} = \frac{s}{\sqrt{n}} = \sqrt{\frac{\sum(y_i - \bar{y})^2}{n(n-1)}}