We had often heard of PID Controller, and of its popularity but basically what is it???
A PID by its abbreviation means Proportional Integral Derivative.
Image Source: Wikipedia
These three terms or systems combine their qualities in such a way that has been in use since 1911 for the application of Automatic Ship Steering and was developed by Elmer Sperry.
Its best implementation is in the fields of Mechanical, Electronic, Communication and many more.
Actually we are surrounded by the PID control systems that have been observed by many few peoples.
A car suspension system is designed in such a way that its spring and shock absorber, does not tends car to oscillate wildly on irregular surfaces and gives us a smooth drive.
Basically there are various parameters in a system which is tuned so that it can perform best according to the conditions.
Just look at the graph and visualize the example of a car described above……
As it is completely observable that here the three constant parameter Kp, Ki, Kd controlling three different systems i.e., Proportional, Integral, Derivative respectively.