Feedback describes the situation when output from (or information about the result of) an event or phenomenon in the past will influence an occurrence or occurrences of the same (i.e. same defined) event / phenomenon (or the continuation / development of the original phenomenon) in the present or future. A well-known example is a typical household thermostat that switches off the boiler when heat expands a bimetal strip. A feedback loop requires three things: a "desired" or pre-programmed state or behavior, some type of sensor to determine whether that state is being achieved, and some mechanism that changes activity if there is a difference between the current state and the preset state.

Feedback is found throughout the living world at all scales: growth, regulation, and response, from the interaction of proteins in cells to the interaction of organisms in complex ecosystems. In the world of technological innovation, feedback is what makes something "smart" whether it is an autopilot on a ship, or a macro software application on a computer, or an automatic climate system in a building.