A radian is a unit for measuring an angle, just like a degree is. To visual a radian, first imagine a circle. Then imagine a line going 1/360th the way around the circle. That is a degree. Now imagine a piece of string connecting the center of the circle with the edge of the circle. The length of that piece of string is the radius of the circle. Wrap that piece of string around the circle. It goes a certain distance around. That angle is a radian. Question: How many radians are there in a circle?