The person in question; the person themselves (used in contexts like identity verification, or referring to the individual concerned).
何か問題があれば本人に連絡してください。
If there is a problem, please contact the person in question.
郵便物は本人しか受け取れない。
Only the person themselves can receive the mail.
本人の同意がなければ情報は開示できない。
Information cannot be disclosed without the person's consent.