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Glossary of Envelope Terms

This page explains the terms and acronyms used the envelope manufacturing industry.

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Aspect Ratio

A USPS® term for describing the length of the envelope divided by the height, where length is the dimension that is parallel to the address.

Augmented Reality (AR) Code

AR code is a live direct or indirect view of a physical, real-world environment in which elements are augmented (or supplemented) by computer-generated sensory input such as sound, video, graphics or GPS data.


Insertable side of an envelope.

Bangtail Envelope

Open side envelope with a perforated piece of paper attached to the top of back panel.

Bankers Flap

A longer, bowed or contoured flap that contributes to the elegance of a bank envelope.

Baronial / Announcement Envelope

Envelope with a pointed v-shaped flap and deep throat on the envelope, used primarily for cards and formal invitations.

Basis Weight

Paper expressed in terms of mass (expressed as weight) per number of sheets. Conventionally measured as the weight of pounds in a ream of 500 sheets.


The die cut paper in the form of an envelope prior to folding.

Blank Converting Press

An envelope folding press that uses die cut paper in the form of an envelope that is folded and glued. 


The spreading or migration of an ink component into an unwanted area. Bleed also refers to documents that have images that touch the edge of a page. A document with bleeds must be trimmed down after printing.

Blind Embossing

A design that is stamped without ink or foil and yields a raised effect in text or an image. 

Booklet Envelope

An open side, double side seam envelope, usually with a wallet-style flap. This envelope comes in many standard sizes.

Bottom Flap

The flap that seals the bottom portion of an open end catalog envelope.

Bright White

Papers with a brightness level of 92 or above.

Business Reply Mail (BRM)

A pre-addressed postcard or envelope that a mail recipient can return to the sender free of charge. The business or organization who sent the pre-addressed postcard or envelope pays standard mailing charges for each mailpiece that is sent back. 

Calendarized Paper 

A type of paper with a smooth, “hard” finish. Ideal for heavy ink designs and 4-color image processes. 

Catalog Envelope

An open end center seam envelope with the seal flap on the short dimension.

Center Seam

The permanent seam that joins the two side flaps together at the center of the envelope, running from the bottom of the envelope to the throat of the envelope. Most commonly seen on an Open End envelope.

Central Impression Print Cylinder 

A single cylinder that supports the paper as it contacts adjacent digital printing plates, yielding tighter print registration, finer screens and print resolution. They are used in multi-color, Enhanced Flexography printing presses for more elaborate, high-quality images.


A type of closure secured to the back side of the envelope with a small reinforced hole punched in the flap to join and secure the clasp in place.

Closed Face

An envelope with no window. Also called a Regular Envelope.


Methods of securing the seal flap to the back of the envelope.

Coated Paper

A paper coated with clay or other white pigments and a suitable binder to produce a smooth glossy or matte finish.


A finish or covering that is printed on paper to provide a protective finish or to add a creative touch.

Coin Envelope

A small open end envelope ranging in size from a #00 – 11/16″ x 2 3/4″ to a #7 – 3 1/2″ x 6 1/2″.

Color Wash

The process of overlaying ink over the entire substrate. Can also be called a flood coat or paint job.

Commercial Envelope

Open side envelope with a commercial-style flap. Sometimes referred to as an “official” envelope.

Commercial Flap

A common bowed or contoured flap with angled shoulders and a scooped throat.  

Courtesy Reply Mail (CRM)

A pre-printed, self-addressed postcard or envelope that a business or organization sends to a recipient, who is responsible for postage if the mailpiece is sent back to the business or organization. The purpose of CRM is to move the mailpiece through mail system with high-speed automation equipment. 

Diagonal Side Seam

A seam running diagonally across the back of the envelope.

Digital Printing Plates

Digital printing plates allow for better, tighter print registration and finer screens. 


A special tool used in manufacturing to cut or shape material. 

Die Cutting

The process of using specialty dies to cut and create envelope blanks.

Double Score

An additional score line placed 1/8″ to 1/4″ up from the regular seal flap to allow the envelope for thicker contents. 

Double Side Seam

A type of seam on an open side envelope where the seams tuck underneath the back panel.


Coloring materials that are soluble in an ink vehicle.

Enhanced Flexography

A style of printing typically used to print 4-color process (CMYK) imagery with a central impression print cylinder for tighter print registration and digital printing plates for finer screens and print resolution on calendarized papers.

Envelope with Foil 

An envelope with foil features both spot and full coverage layers of shiny, aluminum on the envelope. In direct mail applications, spot foil coverage is often used for logos or to highlight special offers while full foil coverage is to enhance the entire look of the mailpiece.

Expansion Envelope

An envelope with gussets that allow it to expand to hold things like books, binders, manuscripts and other bulky items.

Expansion Score

A prepared line on the side seam of an Expansion Envelope to allow it to hold more content.


The address, or non-insertable, side of an envelope.


See Vignettes.


A polystyrene window film and most common, cost-effective envelope window patch. It is postal approved and can be recycled.


Surface of any grade of paper. Can be a high finish (e.g. gloss, smooth).

Flexographic Printing

Method of direct rotary printing using raised image printing plates, affixed to plate cylinders, inked by an anilox roll or doctor-blade- wiped engraved metal roll, carrying fluid inks to substrates.

Foil Liner

A metallic-colored lining placed on the inner part of the flap.


Any folded edge of the envelope. Generally called a side, top or bottom fold.

Four-Color Process or 4-Color Process

Also referred to as CMYK color process, uses four different color inks (e.g. Cyan, Magenta, Yellow and Black) that overlap each other to achieve the full color spectrum. The same four color inks are used to print any multicolor image.


Transparent, highly hydrated paper made from wood products that is used for windows.


Ability of a surface to reflect light.

Grain Direction

The direction of the majority of fibers in a sheet of paper.

High-gloss Ink

Ink that contains special resins and varnishes that produces a glossy appearance when dry.


Imprinted areas on mailpieces representing a method of payment in replacement of a stamp.

Inserting Machine

Equipment that automates the process of stuffing envelopes with contents.

Involvement Devices

An engaging envelope feature that can help increase customer attention and response.

Kraft Paper

Paper with longer and stronger fibers than wove paper, but does not print as well. Available in plain colors and in brown stock.

Lacquer or Varnish

Coatings over printing to protect the print and increase gloss.

Latex Gum

Latex gum is a pressure- sensitive gum applied along the edge of the flap and/or the upper part of the back of the envelope that creates a self-sealing envelope. It has a limited shelf life. Also called Self-adhesive Gum.

Lift Note

A short letter or note from someone other than the author of the letter in a direct mail package. It could be from an editor, manager, company president, expert or creator of the product or service.


A paper or foil covering placed on the inside of an envelope.

Machine Press

A printing press that is native to the envelope converting machine.

Matte Finish

A semi-gloss paper finish.

Metallic Ink

Ink that uses metallic powders, such as aluminum and bronze, mixed with a proper varnish to produce print images with metallic luster.

Metallic Paper

Paper that is covered with an aluminum layer that provides shine, gloss and an attractive metal look. Metallic paper is available in various colors, finishes (e.g. holographic), recyclable and printable (i.e. offset lithography or flexography) for direct mail applications.

Offset Lithography / Offset Printing

An indirect style of printing that produces high-quality prints. Ideal for photographs, halftones and fine screens.

Open End

An envelope with an opening on the shorter dimension.

Open Face / Open Panel

An envelope with a window opening that does not have any type of window film covering the opening.

Open Side

An envelope with an opening on the longer dimension.

Outside Side Seam

A side seam that is gummed on the outside of the envelope.

Pantone® Matching System (PMS)

PMS is a color matching system for selecting ink colors for coated and uncoated papers.

Patch Gum

Adhesive that adheres to the window patch.

Policy Envelope

An open end envelope with the same dimensions as a #10 through #14 commercial envelope.

Polymer Plates

Flexible, direct impression printing plates that are attached to rollers on the envelope machine. Modern polymer plates are thin, yielding crisp imaging and precise registration control.


A translucent envelope window made from petroleum-based products. Filmview and trycite are two types of polystyrene window film.

Post-Consumer Content

The percentage of recycling materials that have been collected from schools, offices and homes and used by the consumer. The content is deinked and repulped for use in the papermaking process.

QR Code

A code consisting of an array of squares that can be scanned and machine read. QR codes are typically used for storing URLs  and  other  information for reading after scanned by a smartphone camera.

Radiation Ink

A type of ink developed to dry instantly. Must be properly handled due to its potential dermal toxicological effects. Ultraviolet ink (UV) and electronic beam (EB) ink are types of radiation inks.

Recycled Paper

Paper that contains fibers from previously manufactured paper that has been processed back to pulp again. Recycled paper may or may not contain post-consumer content.


The method of correlating overlapping colors on one single image.

Regular Envelope

An envelope with no window. Also called Closed Face.

Remittance Envelope

A booklet or side seam style envelope with a deep wallet flap covering most of the back of the envelope.

Remoistenable Gum

A water-soluble adhesive. The most common type of envelope seal.


A prepared line on paper that helps it to fold cleanly.

Seal Flap

The area above the score that folds to close the envelope.

Seal Gum

An adhesive applied to the flap of the envelope in order to create a seal.

Security Tint

Patterned, opaque printing on the inside of an envelope for added security.

Self-adhesive Gum

Latex gum is a pressure-sensitive gum applied along the edge of the flap and/or the upper part of the back of the envelope that creates a self-sealing envelope. It has a limited shelf life. Also called Latex Gum.

Share Mail®

A USPS offering and form of direct mail that provides a mechanism for businesses and organizations to to share information with their customers that can be forwarded on to their customers and other parties without having to affix a stamp. Postage is paid by the account holder who produces and shares the letter or postcard Share Mail mailpiece. Formerly known as Alternate Postage.


The top edge of the inner side seams of the envelope.

Side Seam

A seam that seals the insertable or back side of the envelope when folded. Side seams can be diagonal or perpendicular to the envelope opening. See Double Side Seam.

Specialty Paper

Papers that are available in a variety of colors, finishes, textures and weights.

Spot Colors

Colors generated by an ink (pure or mixed) that is printed in a single run without screens or dots.

Square Flap

A type of flap with a straight edge along the bottom. The most common type of flap. Also called Straight Flap.

Stacked Press

One or more stacks of printing stations arranged vertically on either side of the press frame. Each stack has its own polymer plate cylinder which prints one color of a multicolor impression. 

Straight Flap

A type of flap with a straight edge along the bottom. The most common type of flap. Also called Square Flap.

String and Button

A type of envelope closure that has two round disks riveted to the seal flap and body of the envelope. The two disks are joined by a string twisted in a figure eight. Also called a Tension Tie closure.

Substance Weight

See Basis Weight.

Surface Enhanced White Wove Paper

This is also known as calendarized or super calendarized paper. It features a “hard”, smoother finish and is ideal for heavy ink designs and 4-color processes. Tear-resistant Paper Paper that is near indestructible and will not tear in typical applications.

Tap test

A test used by the USPS to determine if the mailpiece meets regulations. The test is performed when the mailpiece is tapped on the top, bottom, right, and left sides. During a tap test, the delivery address must remain visible in the window with 1/8” clearance at all times.​​​​​​

Tension Tie

A type of envelope closure that has two round disks riveted to the seal flap and body of the envelope. The two disks are joined by a string twisted in a figure eight. Also called a String and Button closure.


Opening at the top of an envelope. The size of the throat is measured from the top edge to the bottom flap to the fold line of the seal flap.


In multi-color print jobs, the overlapping of one color over a different, adjacent color to ensure no white space is visible.


A highly reflective, glossy material that is more brittle and prone to scratches. Sometimes the shine or gloss is too reflective for postal system sorting.


An ultra-lightweight, synthetic paper that is tear resistant and water resistant. When converted on a folding machine, Tyvek envelopes can be used for heavy, bulky and confidential mailings.

Ultraviolet (UV) Ink

A type of radiation ink that consists of pigments dispersed in liquid prepolymers, monomers and initiators that release free radicals which instantly polymerize the ink to a dry, tough thermosetting resin on exposure to intensive UV radiation. The active ingredients in UV inks are more costly than solvents used in conventional inks, and UV inks can be up to three times more expensive than regular inks. 

Varnish or Lacquer

Coatings over printing to protect the print and increase gloss.


An image in which the tones gradually fade away until they blend in with the background they are printed on.

Wallet Flap

A straight, deep flap with a wide gummed area. Offers reliable document protection.

Web Converting Press

An envelope folding press that uses continuous rolls of paper that is cut into single envelope forms, folded and glued.


The open area of an envelope that allows the USPS® and the recipient to read the address or other information.

Window Patch

The transparent film that covers  a window opening on an envelope.

Wove Paper

Paper with short fibers and a soft, smooth surface. Available in multiple weights and colors, this paper prints well.