What does the term ‘zip + 4’ refer to in postal services?

The term 'zip + 4' refers to a 9-digit code that enhances the standard 5-digit ZIP code, providing more precise delivery information. This additional 4 digits help to identify specific locations or addresses within the same ZIP code, such as a particular building, apartment, or section of a street. This system improves the accuracy and efficiency of mail delivery by allowing postal services to sort and route mail more effectively. By using the comprehensive format of 'zip + 4,' postal workers can ensure that mail reaches its intended destination with greater speed and efficiency, which is especially important in densely populated areas where multiple addresses share the same base ZIP code.