According to one of the many definitions in the Cambridge dictionary, a signal is “something that shows something else exists or is likely to happen.” For us that first “something” is generally a change in a measurable quantity such as a voltage, a current, or a pressure, amongst other things, which carries information about the second “something” which may be the heart, or the lung, or the brain. Within the human body, these signals are often those that help us stay alive, such as the signals that regulate the beating of the heart, the inhalation and exhalation of breath from the lungs, or the firing of neurons in the brain.