A radian is defined as the measure of an angle created when the length of the arc it subtends is equal to the radius of the circle. In other words, if you take a circle and draw an arc that has a length equal to the radius of that circle, the angle formed at the center of the circle by the two radii that connect the endpoints of that arc is one radian.
In terms of degrees, one full rotation around a circle (360 degrees) is equal to approximately \(2\pi\) radians. Therefore, one radian is about \(57.3\) degrees.