Explanation: Pulse-width modulation (PWM) is a digital encoding technique where the duration, or "width," of each transmitted pulse is varied in direct proportion to the instantaneous amplitude of the modulating signal. If the modulating signal is strong, the pulse will be wider; if it's weak, the pulse will be narrower. This method is commonly used for controlling power to inertial loads and in digital-to-analog conversion. Amplitude modulation (AM) varies the *amplitude* of a continuous carrier wave. Frequency modulation (FM) varies the *frequency* of a continuous carrier wave. Pulse-height modulation (also known as Pulse-amplitude modulation) varies the *amplitude* (height) of the pulses, not their duration. Therefore, only pulse-width modulation directly matches the description in the question.