What does the term gain mean in amplifiers?

In electronics, "gain" is a broad term used to describe the ability of an amplifier to increase the magnitude of a signal from the input to the output. Depending on the design and purpose of the amplifier circuit, this increase can be measured in terms of voltage, current, or overall power. Because an amplifier takes power from an external supply and uses it to boost the input signal, the ratio of the output signal to the input signal can reflect voltage gain, current gain, or power gain. Therefore, all the provided definitions accurately describe what gain can mean in different amplifier contexts.