Noona is when you decide to slope off for some lunchtime nookie. It is only at lunchtime between the hours of 12-2pm. It can be with someone you know or a new friend.
It is also preferable to have noona in interesting places, like on car bonnets, in parks, on your boss' desk ;) You get the idea.
Having great noona (sex) during the hours of 12-2pm