An accent symbol placing a right-pointing harpoon arrow above expressions to denote vector quantities or mappings.
Examples
Vector notation in geometry
\overrightharpoon{AB} = \overrightharpoon{CD}
Directed line segment or ray
\text{Ray } \overrightharpoon{PQ} \text{ extends infinitely from point P through Q}
Arc notation in circular geometry
\text{Arc measure: } m\overrightharpoon{XY} = 60°