It's the port where you plug in the PC computer in order to set up or configure the system.

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Note added at 17 hrs (2006-04-26 08:35:39 GMT)
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I'm afraid I have to take issue with Zaphod's accusation of nitpicking!

There is a very specific technical difference between 'configuration' and 'calibration', and even if in everyday layman's language we use the latter term imprecisely, in technical translation we certainly cannot risk doing so!

calibration usually translates as étalonnage (sometimes calibrage, in certain specific contexts)

paramétrage can be a bit of a faux ami; paramètre are very often not actually parameters, so much as the settings of those parameters --- and 'paramétrage' is used in this sense by Windows, either for 'settings' or for 'configuration'

So I stand by my 'nit-picking' suggestion from both a linguistic and a technical standpoint --- most public lighting systems aren't likely to need anything much in the way of actual calibration, but certainly will need their settings or configuration downloading / managing from an external computer. Remember that little file tucked away in your root directory: config.sys? It's not 'calib.sys'!