+14 It's the standard unit of meausurement for angles where the complete circle is 2pi rad. This makes dealing with goniometrics h**l of a lot easier!
https://en.wikipedia.org/wiki/Radian
+23251 A 'rad' is a radian, a means of measuring an angle.
There are 2 pi radians in a circle.
Since there are also 360º in a circle, there will be pi radians in one-half of a circle, allowing us to come up with this formula (with R representing radians and D representing degrees:
D / 180 = R / pi
