Post-office box numbers could be referred to as a variety of synonyms depending on the context or the particular region's terminology. Some alternate terms that could be used include P.O. box number, mailbox number, mail drop number, postal code, post office address, and postal box. In certain countries, they might be called a letterbox number, while others could refer to them as a mailbag number or a postbox number. Regardless of the term used, a post-office box number is a unique identifier assigned to someone by the post office to enable them to receive their mail securely and confidentially.