What is caused by a small part of the signal from the amplifier output being sent back to the input of the amplifier?

The phenomenon described, where a small part of the signal from the amplifier output is fed back to the input, is known as feedback. In amplifier circuits, feedback can greatly influence performance and behavior. Feedback is utilized to control gain, stabilize the amplifier, and improve linearity. Positive feedback can lead to increased gain but may result in instability or oscillations if not carefully managed. In contrast, negative feedback is more commonly used to enhance the stability and bandwidth of an amplifier.

Oscillation specifically refers to a situation where the system produces a periodic output without an external input, often as a result of excessive positive feedback. Amplification refers simply to the process of increasing a signal's amplitude, while filtering concerns the selective passage of certain frequencies of signals. Thus, feedback is the term that accurately captures the described scenario, allowing for important functions in electronic circuits that aid in effective signal processing.