For every angle, there exists a line that divides the angle into two equal parts. This line is called the angle bisector.

The interior bisector of an angle is the line or line segment that divides it into two equal angles on the same side as the angle.

The exterior bisector of an angle is the line or line segment that divides it into two equal angles on the opposite side as the angle.

For a triangle, the point where the angle bisectors of the three angles meet is called the incenter.