Which term describes the ratio of an amplifier's output to its input signal?

The term that describes the ratio of an amplifier's output to its input signal is referred to as system gain. System gain quantifies how much an amplifier increases the strength of the input signal, which is crucial in various applications, including medical instrumentation and audio processing. It is typically expressed in a decibel (dB) format, providing an easy way to compare the effectiveness of different amplifiers.

In the context of this question, system gain is fundamental as it directly indicates how effectively an amplifier is performing in increasing the amplitude of the signal it receives, which is essential for ensuring the output can be analyzed or utilized appropriately.

Impedance relates to the resistance faced by the electrical signal within the amplifier but doesn't define the relationship between input and output signals. Display sensitivity concerns how accurately a display can represent subtle changes in input but isn't directly related to the ratio of output to input. CMRR indicates how well an amplifier can reject common mode signals, which are unwanted signals that appear simultaneously on both input terminals; while important in differential signal scenarios, it does not measure the ratio of output to input.