From the aircraft point of view in the UK we'd expect to hear "Gusting" when it's 10 knots more than the average (and yes, a current gust, although it's also good to hear about gust conditions in the last 10 mins!), and "Maximum" when it's less than 10 knots above the average. There's sometimes too high a tendency to use "Gusting" for any wind speed increase - the danger being that it can make pilots unnecessarily nervous, something I see occasionally with students.