From what I've experienced, Asian fusion refers to food that has its roots in traditional Asian cuisine, but is more more modern and is influenced by western tastes, as well. For instance, Peking duck is a very traditional Chinese dish, but hoisin glazed salmon with a spicy fried rice timbale is Asian fusion. Asian fusion restaurants also often serve dishes influenced by more than one Asian country's cuisine. You might end up with Japanese, Korean, Vietnamese and Korean inspired dishes all on the same menu. I've even seen some Chinese-Latin fusion restaurants.
It's all pretty confusing, but it can result in some amazingly inventive and fantastic tasting food.