As shown in the given figure assume that the spring is hung from rigid support like a ceiling. A ball is stuck at the other end of the spring. Now assume that we stretch the spring by pulling the ball and leaving it. It performs oscillations or vibrations. The ball is moving about a fixed point. In the figure position no. 2,4,6,8 and 10 are these positions of the ball. This point is called the mean position. The ball continues its motion on this fixed path at a regular time interval. Its displacement vs time graph is also shown in the figure where displacement is calculated from the mean position on the y-axis and time is on the x-axis. So, the motion of a particle on a fixed path about a fixed point at a regular time interval is called the oscillation or vibration.