Robert Rauschenberg working on his Romances series, 1977, Sidney B. Felsen. © J. Paul Getty Trust. Gift of Jack Shear.
These definitions were drawn from the glossary provided on the National Gallery of Art, Washington Gemini, G.E.L. website. For complete definitions and additional terms, see: https://www.nga.gov/gemini/glossary.htm
What is a print?
Prints are works of art produced in multiple impressions of the same image. They are made by transferring a layer of ink from a printing element, or matrix, onto paper or another material. The matrix can be any material, such as a stone, screen, or metal plate, upon which a design is created for the purpose of transfer. A printing press frequently supplies the pressure for the transfer. The various printmaking techniques are defined by the type of matrix and the manner in which it carries ink. In prints involving more than one color, a separate printing element can be drawn for each color. Multiple colors may be simultaneously printed from a single element and elements may be used many times for different colors.
Intaglio
Printmaking processes, such as aquatint, engraving, etching, mezzotint, and drypoint, in which the image is manually incised or chemically etched into a metal plate using a variety of techniques and tools. One the image is complete, the surface of the plate is covered in ink and then wiped, leaving ink only in the incised marks. The paper receives the ink from the incised recessed marks and not from the top surface of the plate, which has been wiped clean. The paper is dampened so that it will be squeezed under printing pressure into the inked recesses of the plate. One of the distinguishing characteristics of this type of printing is that the dried ink impression stands up from the paper in very slight relief.
Aquatint 
Image: Julie Mehretu working on Auguries, 2010, Sidney B. Felsen. © J. Paul Getty Trust. Gift of Jack Shear.
Aquatint produces effects similar to a watercolor wash. The process entails adhering fine particles of resin to a metal plate as an acid resist. After the plate has been treated in an acid bath, the acid-resistant material is removed (see etching). The resulting etched, or bitten, surface is composed of textured areas of tone rather than lines.
Drypoint
A drypoint line is scratched directly into the copper plate with a sharp metal point, traditionally a needle. As the needle scores the copper, it creates a ridge of metal known as burr on both sides of the incised line, holding ink that will print as a rich velvety line.
Engraving
A metal plate is manually incised with a burin, an engraving tool with a V-shaped metal shaft. Depending on the angle and degree of pressure with which they were scooped out of the metal (usually copper) plate, the incised lines may vary in width and darkness when printed.
Etching
In etching, marks are bitten into the metal plate by chemical action. The plate is coated with a ground impervious to acid through which the artist draws to expose the metal. The plate is then immersed in an acid bath until the open lines of areas are sufficiently bitten. Finally, the ground is removed, and the plate inked and printed.
Mezzotint 
Image: Vija Celmins working on a copper plate for Strata, 1983, Sidney B. Felsen. © J. Paul Getty Trust. Gift of Jack Shear.
In mezzotint, the artist works from dark to light. The plate is systematically roughened with a spur-like tool called a rocker. If inked in this state, it will print a velvety black. Graduated highlights are then smoothed out by scraping and burnishing the plate.
Planographic
Lithography 
Image: David Hockney drawing Billy Wilder on limestone for his Friends series, 1976, Sidney B. Felsen.
© J. Paul Getty Trust. Gift of Jack Shear.
A printing process based on the antipathy of grease and water. The printing elements used are limestone and aluminum or zinc plates, grained to varying degrees of roughness. The image can be produced by photochemical and transfer processes, or be drawn using lithographic crayons and pencils, tusche, chalk, and various grease, lacquer, or synthetic materials. The stone is then washed with a solution, thus chemically producing water-receptive non-printing areas and grease-receptive image areas. The drawing grease is cleaned from the printing surface. The stone is dampened with a wet sponge and a roller bearing greasy printing ink is then rolled over the surface, with the ink adhering only to drawn grease-receptive image areas. Finally, paper is laid on top of the stone or plate, which is passed through a lithography press for transfer.
Screenprint 
Image: Jeff McMane screenprinting a John Baldessari, 2014, Sidney B. Felsen. © J. Paul Getty Trust. Gift of Jack Shear.
A print made by a stencil technique in which ink is forced through stretched mesh fabric onto paper beneath the frame. The image is created by blocking out parts of the mesh in a variety of ways such as hand-painting the screen with glue or lacquer; applying a cutout design; or by painting a light-sensitive resist on the screen which is then developed photographically.
Unlike many of the other printing media, there is no mirror reversal in screenprinting, which is very versatile as it can be placed on almost any material.
Relief
Woodcut
Image: Roy Lichtenstein carving a woodblock, 1980, Sidney B. Felsen. © J. Paul Getty Trust. Gift of Jack Shear.
The artist's design is either drawn directly on the block of wood or on a sheet of paper that is adhered to its surface. A variety of cutting tools can be used to carve away the non-printing areas. When finished, the image will appear as a network of lines and shapes standing out in relief, which are then inked and printed.
Editioning Terms
AP
Artist's proof. A proof that meets the right to print impression or standard used for the edition but is retained apart from the edition by the artist or publisher.
Cancellation 
Image: Ed Ruscha cancelling a plate, 1999, Sidney B. Felsen. © J. Paul Getty Trust. Gift of Jack Shear.
After the edition is printed and signed, the most characteristic “key” element is cancelled or defaced to ensure that no further impression are pulled. When three-dimensional objects are made from a mold, the mold is destroyed after fabrication of the edition.
Chop
Each Gemini publication bears an embossed, dry-stamped, or printed form of the Gemini chop. It is generally placed adjacent to the artist's signature and is accompanied by a copyright mark.
Edition 
Image: Printers Alan Holoubek and Christine Fox, 1981, Sidney B. Felsen. © J. Paul Getty Trust. Gift of Jack Shear.
This is the body of prints or sculpture essentially identical to the right to print (RTP) impression or standard used for the edition or prototype. Two numbers are used in the signing procedure: the upper number follows a consecutive sequence beginning with 1 through the total in the edition (example: 3/25); the lower number indicates the total number of pieces in the edition.
Proof Impressions
Pulled before the printing of the edition in which the development of the image is tracked, and various inks, colors, papers, and other variables are tested.
RTP “Right to proof” or Standard
The first impression achieved in the proofing period that meets the aesthetic and technical approval of the artist and Gemini. It is used as a guide for the production of the edition.
SP “Special Proof”
A proof specifically created for presentation purposes by the artist or publisher that equals the RTP impression.
Gemini G.E.L. and the National Gallery of Art:
“In 1981, the National Gallery in Washington, D.C. honored Gemini with the establishment of a permanent archive. The archive functions as a study center for collectors and scholars. Included in the archive is one proof from each of the over 2300 editions produced, as well as ancillary materials such as shop records and printing elements. Three major touring exhibitions with works from the archive have been organized and exhibited by the National Gallery, and a fourth marking Gemini's 50th Anniversary was on view during the Fall 2015. The online catalogue raisonné provides detailed information on the history of the workshop and all of the artworks in the Gemini archive.”
https://www.geminigel.com/page/national-gallery/