The sound of a quick kiss when voice is also used.Also the sound of lips smacking in a kissing motion... MWAH.. especially expressive over distances of 10+ metres...one of the nicest sounds, very flirty!
The sound of air kissing (to air kiss both cheeks is "mwah mwah")
Also used to describe a chic restaurant or bar frequented by "beautiful people" (esp. media/fashion/art types)