You can find multiple definitions, but I like to use Cyber Physical. These systems are connected to things in the real world.
Operational technology (OT) is hardware and software that detects or causes a change, through the direct monitoring and/or control of industrial equipment, assets, processes and events.
Industrial control system (ICS) is a collective term used to describe different types of control systems and associated instrumentation, which include the devices, systems, networks, and controls used to operate and/or automate industrial processes.
The Industrial Automation and Control Systems (IACS) is a collection of networks, control systems, SCADA systems and other software and hardware systems that can affect or influence the safe, secure, and reliable operation of an industrial process.