What is Modulation? And where Utilized?

Modulation is the process of varying some characteristic of a periodic wave with an external signals.
Radio communication superimposes this information bearing signal onto a carrier signal. These high frequency carrier signals can be transmitted over the air easily and are capable of travelling long distances.
The characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information bearing signal. Modulation is utilized to send an information bearing signal over long distances.