Definitions provided by the United States Postal Service (USPS).

Ancillary service: Forwarding, return, or address correction service included within a mail class. Depending on the mail class, these services are performed at a charge or at no additional charge, if and when the service is actually rendered.

Barcode (BC): A series of vertical bars and spaces that represent any numerical series, most often a correct ZIP Code for the delivery address on a mail piece. The barcode facilitates automated processing by barcode readers and scanners.

Barcode clear zone: A rectangular area in the lower right part of a letter-size mail piece that must be kept free of printing and symbols, except for the barcode itself. This requirement allows automated processing machines to read or apply a barcode.

Carrier Route (CR): The addresses to which a carrier delivers mail. In common usage, carrier route includes city routes, rural routes, highway contract routes, post office box sections, and general delivery units.

First-Class Mail: A class of mail that includes all matter wholly or partly in writing or typewriting, all actual and personal correspondence, all bills and statements of account, and all matter sealed or otherwise closed against inspection. Any mailable matter may be sent as First-Class Mail.

Indicia: Imprinted designation on mail that denotes postage payment (e.g., metered postage or permit imprint).

National Change of Address (NCOA): An address correction service that the USPS provides to mailers through USPS licensees. The licensees match mailing lists against change-of-address information for the entire country from all Computerized Forwarding System units. If a match is made, NCOA can correct the address before it is printed on a mailpiece.

Nonmachinable surcharge: A surcharge on some first-class mail, standard mail, and parcel post pieces that have physical characteristics that prevent the pieces from being processed on automated equipment. Characteristics that make a piece nonmachinable include weight, rigidity, and uneven thickness.

Permit: Any authorization required for specific types of preparation or postage payment. Specifically, an authorization to mail without postage affixed by using indicia or an imprint. Payment is made against an advance deposit account that is established with the USPS for postage and services. Permits also are required to participate in certain programs such as business reply mail.

Presort: The process by which a mailer groups mail by ZIP code so that it is sorted to the finest extent required by the standards for the rate claimed. Generally, presort is performed sequentially, from the lowest (finest) level to the highest level, to those destinations specified by standard and is completed at each level before the next level is prepared. Not all presort levels are applicable to all mailings.

Standard Mail (A): A class of mail that weighs less than 16 ounces. It comprises the subclasses of Regular Standard Mail, Nonprofit Standard Mail, Enhanced Carrier Route Standard Mail, and Nonprofit Enhanced Carrier Route Standard Mail. These subclasses include circulars, printed matter, pamphlets, catalogs, newsletters, direct mail, and merchandise. Standard Mail (A) may be sent at presorted rates and at automation rates.

ZIP Code: A system of 5-digit codes that identifies the individual post office or metropolitan area delivery station associated with an address. ZIP +4 is an enhanced code consisting of the 5-digit ZIP code and four additional digits that identify a specific range of delivery addresses.