What is a radian?

What the heck is a radian anyway? Most students understand what a degree is, but a radian causes a lot of confusion. Recall that pi is the number of times the diameter of a circle would fit around the circumference. Imagine cutting a string to the length of the radius of a circle. Then lay this string along the circumference. The angle created by connecting a line from the center of the circle to each side of the string is a radian.