In printing, a stereotype, also known as a cliché, stereoplate or simply a stereo, was a "solid plate of type metal, cast from a papier-mâché or plaster mould (called a flong) taken from the surface of a forme of type" and used for printing instead of the original.
In the days of set movable type, printing involved placing individual letters (called types) plus other elements (including leading and furniture) into a block called a chase. Cumulatively, this full setup for printing a single page was called a forme. Ink was then applied to the forme, pressed against paper and a printed page was made. This process of creating formes was labor-intensive, costly and prevented the printer from using their types, leading, furniture and chases for other work. Furthermore, printers who underestimated demand would be forced to reset the type for subsequent print runs.
By creating a stereotype, printers could easily reprint documents and free their equipment for other work. The stereotype thus changed the way books, especially novels, magazine articles and other popular forms of literature were reprinted, saving printers the expense of resetting while freeing the type for other jobs.
... while Nathaniel Hawthorne's publishers assumed that The Scarlet Letter (1850) would do well, printing an uncharacteristically large edition of 2,500 copies, popular demand for Hawthorne's controversial "Custom House" introduction outstripped supply, prompting Ticknor & Fields to reset the type and to reprint another 2,500 copies within two months of the first publication. Still unaware that they had an incipient classic on their hands, Ticknor & Fields neglected at this time to invest in stereotype plates, and thus were forced to pay to reset the type for a third time just four months later when they finally stereotyped the book.
English sources often describe the process as having been invented in 1725 by William Ged, who apparently stereotyped plates for the Bible at Cambridge University before abandoning the business. However, Count Canstein had been publishing stereotyped Bibles in Germany since 1712 and an earlier form of stereotyping from flong was described in Germany in 1702. It is even possible that the process was used as early as the fifteenth century by Johannes Gutenberg or his heirs for the Mainz Catholicon. Wide application of the technique, with improvements, is attributed to Charles Stanhope in the early 1800s. Printing plates for the Bible were stereotyped in the US in 1814.
Over time, stereotype became a metaphor for any set of ideas repeated identically or with only minor changes. In fact, cliché and stereotype were both originally printers' words, and in their printing senses became synonymous. However, cliché originally had a slightly different meaning, being an onomatopoeic word for the sound that was made during the process of striking a block into molten type-metal during another form of stereotyping, later called in English "dabbing".