In 1964 the Print Council of America defined an original print as follows:
"An original print is a work of art, the general requirements of which are: (1) The artist alone has created the master image in or upon the plate, stone, wood block or other material for the purpose of creating a print. (2) The print is made directly from the said material, by the artist or pursuant to his direction. (3) The finished print is approved by the artist.
When an artist makes a serigraph, he usually prints a definite number that he has decided in advance, or an edition of serigraphs. These are duplicates or near duplicates of the same master stencil. There will always be some variation among the prints in any one edition. A print that differs considerably from the other is not included in the signed edition. It may be saved and gain value as a unique print, especially if it is a good one. Occasionally an artist holds on to prints produced during the evolution of the edition. These generally differ somewhat from the edition and are labeled proof prints."
Silk-Screen Printing for Artists & Craftsmen by MathildaV. Schwalbach & James A. Schwalbach
For more information and reading:
Print Council of America
International Fine Print Dealers Association (ifpda)