PID Control stands for Proportional-Integral-Derivative feedback control and corresponds to one of the most commonly used controllers used in industry. It's success is based on its capacity to efficiently and robustly control a variety of processes and dynamic systems, while having an extremely simple structure and intuitive tuning procedures. Although not comparable in performance with modern control strategies, it is still the best starting point when one has to start designing the autopilot.
The working principle behind a PID controller is that the proportional, integral and derivative terms must be individually adjusted or "tuned." Based on the difference between these values a correction factor is calculated and applied to the input.