Why is the motion of simple pendulum oscillatory?

Ans: If an object in periodic motion moves in such a way that in half of its time period its motion is in a definite direction and in other half of the time period its direction of motion is opposite but the path is same then its motion is called oscillatory.

A simple pendulum moves in one direction in half of its time period and moves in the same path but in opposite direction in the second half of time period. For this reason motion of simple pendulum is oscillatory.