When the system is able to control itself.
May use feedback received to match against goals and objectives. If any discrepancies detected, system takes corrective action by changing outputs which, as a result, change the inputs.
This occurs on a continuous basis depending on the feedback.
Control is over-arching term that includes feedback.
Control loop sometimes talked about rather than feedback loop.
Important aspect of control is preventive control.
Example: Computer security systems.
Feedback would be running a virus removal tool on detection of a virus in the system.
Control would be examining the inputs to prevent the virus from entering the system.