What is the term that describes a device's ability to amplify a signal?

The term that describes a device's ability to amplify a signal is "gain." Gain measures how much a device increases the amplitude of a signal from its input to its output. It is an essential characteristic of amplifiers, where the goal is often to take a weak signal and produce a stronger output that can drive speakers, transmit over long distances, or be processed further. Gain can be expressed in various ways, including as a ratio (output power/input power) or in decibels (dB), which provides a logarithmic representation of the amplification factor.

In contrast, the other terms listed do not relate specifically to amplification. Forward resistance refers to the resistance encountered when current flows through a semiconductor device, which affects current and voltage characteristics but is not a measure of amplification. Forward voltage drop indicates the voltage loss across a semiconductor device when it is in operation, again not measuring amplification. On resistance refers to the resistance of a device when it is turned on but does not pertain to the concept of signal amplification.