Perpendicular Bisector

Perpendicular- lines in the same plane that intersect at 90 degree angles.
Bisector- a line that divides another line segment in half and meets at right angle. 
-equal line segments are shown with hash marks.
Perpendicular Bisector- a line that divides another line segment in half and meets at right angle. 

-equal line segments are shown with hash marks.

Here's a link on Perpendicular Bisectors.