Definition:Angle Bisector

Definition

 * AngleBisector.png

Let $\angle ABC$ be an angle.

The angle bisector of $\angle ABC$ is the straight line which bisects $\angle ABC$.

In the above diagram, $BD$ is the angle bisector of $\angle ABC$.

Thus $\angle ABD \cong \angle DBC$ and $\angle ABD + \angle DBC = \angle ABC$.

Also known as
The angle bisector of an angle can also be referred to just as the bisector if the angular nature of its object is understood.

An older term for the same thing is bisectrix.