where one has gone to; place one has gone to; (outing) destination
外出先で急用ができた。
An urgent matter came up while I was out.
外出先を必ず事務所に連絡してください。
Please be sure to inform the office where you will be.
彼女は外出先で緊急のメールを受け取った。
She received an urgent email while she was out.