The perpendicular bisector of a side of a triangle is a line perpendicular to the side and passing through its midpoint.
The three perpendicular bisectors of the sides of a triangle meet in a single point, called the circumcenter.
The circumcenter is equidistant from the vertices of the triangle. (See circumcenter theorem.)
The angle bisector of an angle of a triangle is a straight line that divides the angle into two congruent angles.
The three angle bisectors of the angles of a triangle meet in a single point, called the incenter.