Any Motion that repeats itself at a regular interval of time on the same path is known as Periodic Motion.

Oscillation refers to any Periodic Motion moving at a distance about the equilibrium position and repeats itself over and over for a period of time.

Simple Harmonic Motion (SHM) is a Periodic motion in which the acceleration of the particle is directly proportional to its displacement from the mean position of rest and is always directed towards the equilibrium.

In ideal case, an oscillator should keep oscillating for infinite time span.

Because the total energy is conserved. A damped oscillation is an oscillation in which the amplitude fades away with time. It happens due to the presence of opposing force or the

retarding force such as friction.

Example of oscillations can be very easily seen in our everyday lives as like the movement of the pendulum of the clock represents oscillation, a guitar string which produces music also oscillates.