In printmaking, an edition is a number of prints struck from one plate, usually at the same time. This may be a limited edition, with a fixed number of impressions produced on the understanding that no further impressions (copies) will be produced later, or an open edition limited only by the number that can be sold or produced before the plate wears. Most modern artists produce only limited editions, normally signed by the artist in pencil, and numbered as say 67/100 to show the unique number of that impression and the total edition size.
An important and often confused distinction is that between editions of original prints, produced in the same medium as the artist worked (e.g., etching, or lithography), and reproduction prints (or paintings), which are photographic reproductions of the original work, essentially in the same category as a picture in a book or magazine, though better printed and on better paper. These may be marketed as "limited editions" with investment potential (which is rarely realized), and even signed and numbered by the artist. Some knowledge is often required to tell the difference.
One of the main reasons for the development of printmaking was the desire of artists to make more money from their work by selling multiple copies; printmaking satisfies this motive. The production of multiple copies also tends to reduce production costs and market price when compared to a single or unique image. Until the 19th century, in the period of the Old master print the concept of an edition did not really apply to prints, unlike books. Prints were often run off as demand allowed, and often worn-out plates were reworked by the original artist or another, to produce a new state. The art market attempts to distinguish between "lifetime impressions" and "late impressions", which were produced after the death of the artist. This can be done to some extent by the study of the paper involved, and its watermark, and the condition of the plate as revealed by the printed image. But it remains a difficult area.
The aquatints of Goya, which are done in a technique that wears out quickly on the plate, were the first important prints to be published initially in limited editions, which however were not signed or numbered. In fact the plates survived, and since Goya's death several further editions have been published, showing a progressive and drastic decline in quality of the image, despite some rework. Because of this and other cases, "posthumous editions" produced after the death of an artist, and obviously not signed by him, are usually far less sought after. The plates of later prints are often "cancelled" by defacing the image, with a couple of impressions of the cancelled plate taken to document it. This is now expected by collectors and investors, who want the prints they buy to retain their value.