(i) Periodic motion. A motion that repeats itself after a fixed interval of time is periodic motion.
(ii) Oscillatory motion. To and fro motion of an object about a fixed mean position is oscillatory or vibratory motion.
(iii) Oscillation. The motion of the pendulum from one extreme position to another extreme position and back to the first extreme position is one complete oscillation.
(iv) Time period. The time taken by a vibrating particle to complete one oscillation is called the time period of the pendulum.
