In printing, a stereotype, also known as a cliché, stereoplate or simply a stereo, was originally 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" used for printing instead of the original.
The compositing of individual cast metal sorts of type into lines with leading and furniture tightly bound into a page forme was labor-intensive and costly. The printer would incur further expense through loss of the sorts for other uses while held in formes. With the growth in popularity of the novel, printers who did not accurately predict sales were forced into the expense of resetting type for subsequent editions. The stereotype radically changed the way novels were reprinted, saving the printer's recompositing expense while freeing the sorts 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.
Stereotyping was invented by William Ged in 1725, who apparently stereotyped plates for the Bible at Cambridge University before abandoning the business. 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, this became a metaphor for any set of ideas repeated identically, en bloc, with minor changes. In fact, cliché and stereotype were both originally printers' words, and in their literal printers' meanings were synonymous. Specifically, cliché was an onomatopoeic word for the sound that was made during the stereotyping process when the matrix hit molten metal. This was known as 'dabbing' in English. Precisely, the forme was placed on molten lead at the point of cooling to make the cast.
The term "stereotype" derives from Greek στερεός (stereos) "solid, firm" and τύπος (tupos) "blow, impression, engraved mark" and in its modern sense was coined in 1798.