An electronic process control is a system of electronic sensors wired to a computer that controls a complex industrial system.
A big example is a nuclear power station. Just think of the operations room where they control the power station. It is filled with buzzers, lights, computers and maintained around the clock. The system is far too complicated for humans to respond to changes as they occur. Basically, the computers control the constant minor adjustments that have to be made to valves, injection devices, heating levels, water pumping and many other variables. If there is a problem, then the electronic process control will sound an alert to warn the operations staff on duty and they will follow their procedures to work in conjunction with the computer control.
Another example is the internet. Computers control the internet by determining the best route for the data to take around the world. The controlling computers much know the level of data being transmitted through different parts of the internet and then send new data in the direction of the clearest logical path.