The character in the title is the Chinese character for nine, and the clip is simply its Mandarin pronunciation, jiu, spoken as a standalone sound. Short single-word clips like this circulate on soundboards because they are easy to search, drop into an edit and reuse across languages without needing context. It is most useful as a counting sound or a language-learning cue, and its brevity is part of its appeal: at under half a second it can mark a moment without interrupting the flow of a video or stream.