noun, noun which may take the genitive case particle 'no'
another matter; separate case; different issue
Used to indicate that something is a different topic, case, or project from the one currently under discussion. Often used in business or formal contexts.
それは別件で、今話していることとは関係ありません。
That's a separate matter and has nothing to do with what we're discussing now.
別件の打ち合わせが入ったので、先に失礼し
I have a meeting for another project, so I'll excuse myself first.