Fiu fiu is the written form of a two-note wolf whistle long used to signal attraction or approval, and in meme edits it has merged with aura, the slang for someone's cool, confident presence. This short version, stretched spellings and all, circulates on soundboards and in short videos as a quick hype reaction. Its popularity comes from how instantly readable it is: two whistles need no context, and the shouted aura turns a compliment into an exaggerated joke about style, confidence and presence.