A back-and-forth motion of matter is called oscillation. It is a periodic motion where the matter moves away from a central point, reaches a maximum displacement, and then returns to the central point, only to move away in the opposite direction, reaching another maximum displacement, and then returning to the central point again. This pattern of motion repeats itself over time, creating a back-and-forth movement. Examples of oscillation include the swinging of a pendulum, the vibration of a spring, or the alternating current in an electrical circuit.