I'm not sure what you mean by "HIYUN.VT". This doesn't appear to be a common word, phrase, or standard file name. It could potentially be:

1. A misspelling of something else

2. A specific file name or code for a particular system or program

3. An internet slang term I'm not familiar with

Could you please provide more context or clarify what you're asking about? If it's related to a specific field or software, letting me know might help me understand better and provide a more useful response.