process control usually refers to the continuous control of industrial (chemical, and other) processes. Nowerdays this is frequently done with computer based systems (like ABACUS4 amongst many others).
30 years ago (when I started working in the industry) almost all process control was done using pneumatic controllers. Electronic controllers were becomming very popular, and computers were something very expensive that research departments played with.
Computerised process control was then high tech, and the best brains worked on it. Now sadly the best brains amuse themselves elsewhere.