The increase in signal level by an amplifier is called:

In electronics, the term used to describe the increase in signal level (voltage, current, or power) provided by an amplifier is 'gain'. It represents the ratio of the output signal to the input signal and is typically expressed in decibels (dB). The other options describe entirely different concepts. Attenuation is a decrease in signal level, modulation is the process of adding information to a radio carrier wave, and amplitude describes the raw strength of a signal at a given moment, not the measure of its increase.