'PID' stands for Proportional-Integral-Derivative in process control. It is a type of control loop feedback mechanism widely used in industrial control systems. A PID controller adjusts a control input based on three parameters—proportional, integral, and derivative—to minimize the error between a desired setpoint and a measured process variable. Each term contributes differently: the proportional term reacts to current error, the integral term considers past errors, and the derivative term predicts future errors. This allows for optimized process control, ensuring stability and desired performance in various applications.