A motion which repeats itself after a fixed interval of time is called periodic motion. There are two types of periodic motion:
The motion of the hands of the clock is non-oscillatory but the to and fro motion of the pendulum bob is oscillatory. However, both the motions are periodic.
An oscillatory motion is normally periodic but a periodic motion is not necessarily oscillatory. A motion which repeats itself in equal intervals of time is periodic and if it is about a mean position, it is oscillatory.
The earth completes its rotation about its own axis in 24 hours and days and nights are formed. It also revolves around the sun and completes its revolution in 365 days. This motion produces a sequence of seasons. Similarly all the planets move around the Sun in elliptical orbits and each completes its revolution in a fixed interval of time. These are examples of periodic non-oscillatory motion.