Oscillatory motion is periodic to and fro motion.

Explanation:
Oscillatory motion refers to the repetitive back and forth motion of an object about a certain equilibrium position. It can occur in various systems such as mechanical systems, electrical systems, and even in waves.

- Periodic motion: Oscillatory motion is a type of periodic motion, which means that it repeats itself after a certain fixed interval of time. The object or system undergoing oscillatory motion moves to a certain point, then returns to its initial position, and continues this cycle repeatedly.

- To and fro motion: Oscillatory motion is characterized by the back and forth motion of an object or system. It moves away from its equilibrium position, reaches a maximum displacement, and then reverses its direction to move towards the equilibrium position. This motion continues in a cyclic manner.

- Equilibrium position: In oscillatory motion, there is an equilibrium position around which the object or system oscillates. The equilibrium position is the point where there is no net force acting on the object, and it is the position towards which the object tends to return.

- Examples: Some common examples of oscillatory motion include the swinging of a pendulum, the vibrations of a guitar string, the motion of a simple harmonic oscillator, and the back and forth motion of a mass-spring system.

In summary, oscillatory motion is characterized by periodic to and fro motion of an object or system about an equilibrium position. It is a fundamental type of motion observed in various systems and has applications in many fields of science and engineering.