 – system where only the inputs and outputs can be viewed, and not its implementation (see "experiment model")

 – Study of regulatory and purposive systems

 – Kind of handshake or communication that occurs as two or more objects have an effect upon one another

 – Process of repeating items in a self-similar way

 – Tendency to oscillate at certain frequencies

 – Cyclic structure that goes through several levels in a hierarchical system.

 – Outcomes of a purposeful action that are not intended or foreseen