A horizontal line placed above text or expressions to denote line segments, closure operations, or averages in geometry and analysis.
Examples
Line segment notation in geometry
\text{Length of line segment AB: } |\overline{AB}| = 5 \text{ units}
Complex conjugate notation
z = 2 + 3i, \quad \overline{z} = 2 - 3i
Mean value in statistics
\overline{X} = \frac{1}{n}\sum_{i=1}^n X_i