Internal and external angle

As an interior angle of a ( closed ) refers to a geometric figure enclosed by two sides of angle, which lies within the figure. So one angle is always at a corner of the figure.

Properties and Related Terms

A -gon has interior angles.

The angle sum theorem states that the sum of the interior angles of a pentagon in Euclidean geometry is constant.

A circle or an ellipse or similar has no internal angle.

A side angle of an interior angle is called the exterior angle.