What is a radian?

A radian is the angle in a segment that gives an arc length of 1 radius. This is another way to measure angles instead of degrees. As the circumference of a circle is 2pir, we have 2pi radiuses in the circumference. In terms of angles, this means that in 360 degrees we have 2pi radians, so we can use this to solve that 1 radian = 180/pi.