Japanese phrase
私用です。 shi yō de su
Meaning
It's a personal matter.
When to use it
States that the matter is personal. It politely avoids giving specific details and suits situations where a short, reserved answer is appropriate.
Example dialogue
こちらへはお仕事で来られたんですか？ ko chi ra e wa o shi goto de ko ra re ta n de su ka
Did you come here for work?
私用です。 shi yō de su
It's a personal matter.