NIST defines an Industrial Control System as “an information system used to control industrial processes such as manufacturing, product handling, production and distribution. Industrial control systems include supervisory control and data acquisition systems used to control geographically dispersed assets, as well as distributed control systems and smaller control systems using programmable logic controllers to control localised processes”.
Using an extremely simple example, a home heating system will collect data from a thermostat. It will perform a function based on that data using a set of established parameters to adjust the heating within the house accordingly. If the thermostat where to fail, what would happen? In an industrial context, failure of a safety system could not only stop production, in extreme scenarios, it could cause loss of life.