@mhoye 'Data port' is probably meant for Ethernet, although it may or may not be connected. Ethernet connectivity used to be quite common in Irish hotels, and has not entirely gone away yet.

But it might also have be meant to connect a modem, in the times of dial-up. Modem connectors tended to use the narrower RJ11 connectors way-back-when, but RJ45 with only the middle positions populated was not unheard of, and IIRC, there was a bit of a push to popularise RJ45 for phone lines in the early noughties.