Yep = hose connector. If have exactly same part in my boat, connected behind the scenes to boat's pressurised freshwater, so I can plug in a hose and wash tenders using fresh water. But the same part can be used to plug in a dock hose so that you have pressurised dock water in all the taps in the boat, when you're in harbour.
As suggested, it could be a pumped deck-wash. Some modern boats also have a similar connector for "shore water" - like shore power but to allow you to connect up a hose to an external tap and feed fresh water direct to the taps without going through the tank. Our previous boat (Beneteau) had one, but none of the marinas would allow us to connect it for H&S reasons.