what is PWM mudulasun.?

Answer 1

Pulse-width modulation (PWM) of a signal or power source involves the modulation of its duty cycle, to either convey information over a communications channel or control the amount of power sent to a load.

PWM power supplies are typically more efficient than linear power supplies, but they make "electrical noise" which may affect other electronics.

Or as the link below better details, PWM is used for things like remote control or other communications.