An angle whose vertex lies outside of the circle, but whose sides touch the circle is a

Exterior angle.

Step-by-step explanation:

An exterior angle can be defined as those angles with vertex outside the circle, but the sides of the angle formed intercep the circle as tangents or secants.

Additionally, we can find the measure of an exterior angle by dividing by two the difference between the intercepted arcs.

Therefore, the right answer is exterior angles.