Signals and Systems: In signal processing, a signal is a function that conveys information about a phenomenon. In electronics and telecommunications, it refers to any time-varying voltage, current or electromagnetic wave that carries information. A signal may also be defined as an observable change in a quantity.
Signals and Systems GATE MCQ: Any physical quantity that exhibits variation in space or time can be a signal used, among other possibilities, to share messages between observers. According to the IEEE Transactions on Signal Processing, a signal can be audio, video, speech, image, sonar and radar-related and so on. In a later effort of redefining a signal anything that is only a function of space, such as an image, is excluded from the category of signals. Also, it is stated that a signal may or may not contain any information.