An indeterminate, very distant, or impossible future date; a never-never day; when pigs fly.
这件事情他答应会帮忙，但具体什么时候能完成，我看真是要等到驴年马月了。
He promised to help with this matter, but as for when it can be completed, I really think it will be a very long time from now, if ever.
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