Personal affairs; private matters (matters concerning an individual rather than public/business matters).
これは私事なので会社に話すわけにはいかない。
This is a personal matter, so I can't tell the company about it.
彼女は私事で休暇を取った。
She took time off for personal reasons.
結婚は私事だが、上司には報告しておいた方がいい。
Marriage is a private matter, but it's better to inform your boss.
Personal secrets; privacy — private information one does not want others to know.
私事を詮索するのは失礼だ。
It's rude to pry into someone's private affairs.
日記は完全な私事だ。
A diary is entirely private.
家族の私事を外部に話してはいけない。
You must not disclose your family's private matters to outsiders.