The motion of a vibrating body is called simple harmonic motion (SHM) when the acceleration directly changes with the displacement of the body from the mean position and is always oriented to the mean position.
Examples:
A pendulum’s motion is a S.H.M.
An S.H.M. is the motion of a vibrating mass connected to a spring.
Final answer:
Hence, the simple harmonic motion is defined and the examples are given above.