The term was first proposed by Norbert Wiener in the book referenced below. Originally, cybernetics drew upon electrical engineering, mathematics, biology, neurophysiology, anthropology, and psychology to study and describe actions, feedback, and response in systems of all kinds. It aims to understand the similarities and differences in internal workings of organic and machine processes and, by formulating abstract concepts common to all systems, to understand their behaviour.
Modern "second-order cybernetics" places emphasis on how the process of constructing models of the systems is influenced by those very systems, hence an elegant definition - "applied epistemology".
Related recent developments (often referred to as sciences of complexity) that are distinguished as separate disciplines are artificial intelligence, neural networks, systems theory, and chaos theory, but the boundaries between those and cybernetics proper are not precise.
See also robot.
["Cybernetics, or control and communication in the animal and the machine", N. Wiener, New York: John Wiley & Sons, Inc., 1948]