Many cars have settings which are not very well known. Often features are simply overlooked by owners who have never found the option, while others are sometimes hidden away by unlocking certain button sequences.
However most cars have another category of options totally hidden and unknown to the average owner. Most modern cars have numerous control units dotted around the vehicle which all perform their respective functions while often communicating to each other. Most of these control units will be intended for use in vehicles with differing options, and sometimes even for completely different models.
In order to cut down producing loads of slightly different controllers, instead often there will be various parameters set in these various control modules which specify which options have been fitted. Often these coding procedures will only function if various relevant parts have been fitted, and setting incorrect coding can often create errors or even permanently damage the controller.
The procedure itself I normally refer to as coding, although I have heard mechanics refer to the procedure as programming. My personal preference is to reserve that word for tasks such as flashing an ECU.
Some examples of various tasks that can be done by changing settings in control units:
Retrofit Cruise Control (Fit stalk then code settings)
Retrofit Xenons (Fit lights and all electrics then code settings)
Retrofit LEDs (Change lights and code)
Retrofit Folding Mirrors (Fit mirrors, wiring, maybe new control modules then code settings)
Retrofit Park Sensors (Fit bumpers, sensors, wiring, controller, then code settings)
Change Alarm Beeps (Just coding if available)
Window Closure from Key (Just coding if available)
Mirrors Folding from Key (Just coding if available)
Follow Me Home Lights (Just coding if available)
Remove Speed Limiters (Just coding if available and legal)
These are just a handful of example of the many tweaks that are available. For many cars there are reasonably priced interfaces available that allow all kinds of changes, while for some brands, only the main dealer tools allow full access.
This thread is meant to be a general introduction to the idea. For anyone intending on how to get started out, this is the thread, I hope this will spawn numerous other manufacturer specific threads, where I hope to help in a few.