A placebo button (also referred to as an idiot button) is a push-button with apparent functionality that actually has no effect when pressed. They are commonly placed in situations where it would have once been useful to have such a button but the system now proceeds automatically.
Although non-functional, the buttons can give the user an illusion of control. In some cases the button may have been functional, but may have failed or been disabled during installation or maintenance or was, in a relatively small number of cases, installed to keep people contented, much in the same way as placebos.
In many cases a button may appear to do nothing but in fact cause behavior that is not immediately apparent; this can give the appearance of it being a placebo button.