Definition: An angle whose measure is greater than 90° and less than 180°

Try this
Adjust the angle below by dragging the orange dot at A and see how the angle ∠ABC behaves.
Note that it is obtuse for all angles greater than 90° and less than 180°

Not to be confused with an obtuse triangle which has one obtuse interior angle.

Types of angle

Altogether, there are six types of angle as listed below. Click on an image for a full description of that type and a corresponding interactive applet.