The motion of a swing is a combination of linear motion and rotational motion. As a person swings, the seat of the swing moves in a circular path, while the person's body moves up and down in a linear path. The speed of the swing also changes throughout the motion, as the swing moves faster at the bottom of its arc and slower at the top.
Therefore, the motion of a swing can be described as variable, as both the direction and the speed of the swing change throughout the motion.