In signal processing, a signal is a varying physical quantity that conveys information or carries energy. A signal can be in the form of a voltage, current, or electromagnetic wave. It can represent various types of information such as speech, video, or data. Signals are processed using various techniques such as filtering, modulation, demodulation, amplification, and coding to extract the desired information from the signal. Signal processing is a crucial aspect of many applications including communication systems, control systems, medical devices, and consumer electronics. Signals are also used to represent the inputs and outputs of a [[system]].