A 180-degree angle is called a straight angle. Angles that are exactly 90 degrees are called right angles, while those that are between 0 and 90 degrees are called acute. Angles that are between 90 and 180 degrees are considered obtuse.
Once an angle is larger than 180 degrees, it is categorized as a reflex angle. As a reflex angle turns one full rotation of 360 degrees, a circle is formed.
Angles are created when two straight lines intersect. The place where the two lines meet is called the vertex, while the two lines are called the arms of the angle. Rotating one of the arms either increases or decreases the angle measurement depending upon the direction of rotation.