What is meant by the term "two radians"?

By creating a circle of radius r with its center at the angle's vertex, one may establish the radian measure of an angle. The letter s stands for the length of the arc on the circle that the angle defines. The ratio s/r is used to measure angles in radians.
When positioned in the center of a circle of radius r, an angle of 2 radians slices off an arc of length 2r.