Consider a system which is at rest initially. When this human is displaced slightly from its mean position and released, then it begins to oscillate from its mean position. These oscillations are called as oscillations or natural oscillations. The frequency with which the system vibrates is known as the natural frequency. The oscillations arise due to the restoring forces set up by the system internally.
Trend is a trend of reproduction of power. It is a process of transfer of power in a method by means of interference due to the recurring regular movement of the contaminants of the method about their mean place in which the power is passed over from one compound to another compound without the contaminants actually making their mean roles.