What causes droop in control theory?

[Maharshi Roy]

In control theory, we have the proportional controller which is of the form-
u(t) = ke
where e is the error between the current measured value and the required value. The P controller is said to droop. To avoid this, an integral term and a differential term is added. What is this droop?
I read it in wikipedia but couldn't understand.
http://en.wikipedia.org/wiki/Droop_(control)

 

[Greg Bernhardt]

Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?

 

[FactChecker]

A simple proportional feedback will not completely drive the error to zero. Given a step input, an error will remain and approach a constant. That is the "droop".