- 90° — Right Angle
- 0° - 90° — Acute angle
- 90° - 180° — Obtuse angle.
- 180° - 360° — Reflex angle.
Angles are also sometimes expressed in radians, with 2 * Pi radians representing an entire revolution. A radian is therefore just over 57 degrees.
Pi itself is defined as the ratio of the circumference to the diameter for a circle. See also the separate entry for 'Pi'.