

Oscilltory motion refers to any motion which repeats itself over a period of time, whereas the Harmonic motion is a motion in which a force causes.
The equation for harmonic motion, the force is directly proportional to displacement to power n, when force is proportional to displacement or n =1. It is called simple harmonic motion or SHM. So basically, every SHM is oscillatory but every oscillatory is not SHM.
