"Nani" is the Japanese word for "what," and online it became a staple reaction sound through anime clips, compilations, and meme edits shared across YouTube, TikTok, and Discord. Many users search it as "noni" because of mishearing or phonetic spelling, but the meme usually refers to the dramatic surprised delivery of "nani?" Its popularity comes from how quickly it communicates confusion and disbelief. It remains common in short-form edits because the sound is instantly recognizable even when the source scene is not.