This term refers to the unhyphenated English word "cooperation" often being changed to "Cupertino" by older spellcheckers with dictionaries containing only the hyphenated variant, "co-operation". Cupertino is notable for being the home of Apple Inc.
"Cupertino" has been in Microsoft's custom dictionaries since at least 1989 (when Word 4 for Mac was released). Lack of vigilance in post-spellcheck editing can result in even official documents containing phrases such as "as well as valuable experience in international Cupertino" and "reinforcing bilateral and multinational Cupertino and assistance actions." Other examples include "South Asian Association for Regional Cupertino" and "presentation on African-German Cupertino."
Benjamin Zimmer of Thinkmap, Inc. and the University of Pennsylvania has collected many examples of similar errors, including the common replacement of "definately" (misspelling of "definitely") with "defiantly," DeMeco Ryans with "Demerol" (in the New York Times), Voldemort with "Voltmeter" (Denver Post), and the Muttahida Qaumi Movement being replaced with "Muttonhead Quail Movement" (Reuters).
The user need not always select an incorrect word for it to appear in the document. In WordPerfect 9 with factory default settings, any unrecognized word that was close enough to exactly one known word was automatically replaced with that word. Current versions of Microsoft Word come configured to "auto-correct" misspelled words silently as the user types. Smartphones with dictionary supported virtual keyboards automatically replace possible mistakes with dictionary words.
See also 
- "Medireview", an erroneous correction of the word medieval in Yahoo! Mail in 2001.
- Predictive text; discusses textonyms, words with the same keypad sequence which may thus be confused in an SMS
- Scunthorpe problem, false positives in obscenity filters
- "When Spellcheckers Attack: Perils of the Cupertino Effect", OUPblog, Oxford University Press, November 1, 2007.
- "The Cupertino effect", Language Log, March 9, 2006.
- Cooperation Between India And South Africa In The Wider Interests Of Indian Ocean Region And The World[dead link]
- Report on meetings of the Deputy Ministers of Defence[dead link]
- "The word: Cupertino effect". New Scientist. 2007-12-01. p. 62.
- "Cell phone cupertinos", Language Log, August 23, 2010.
- The word: Cupertino effect, New Scientist (subscription only; hard copy in issue of December 1, 2007, p. 62)
- "Cupertino casts spell on computer spellcheckers," Cupertino Courier, by Hugh Biggar,